Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data

Transcription

1 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Amirhossein Moshirsalimi November, 2010

2 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data By Amirhossein Moshirsalimi Thesis submitted to the International Institute for Geo-information Science and Earth Observation in partial fulfilment of the requirements for the degree of Master of Science in Geo-information Science and Earth Observation, Specialisation: Geo-Informatics (GFM) Thesis Assessment Board Chairman: Prof. Dr. M.J. Kraak External examiner: Dr. Ir. R.J.A. van Lammeren Supervisor: Ms. Dr. C.A. Blok Second supervisor: Dr. O. Huisman Advisor: Ms. Q. Zhang MSc INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION ENSCHEDE, THE NETHERLANDS

3 Disclaimer This document describes work undertaken as part of a programme of study at the International Institute for Geo-information Science and Earth Observation. All views and opinions expressed therein remain the sole responsibility of the author, and do not necessarily represent those of the institute.

4 Abstract Nowadays, the transportation systems play an important role in human life. By increasing cities and population, transportation networks have become greater and more complex than before. For controlling traffic in roads, transportation planners and managers need some maps about traffic situations of the road network to diagnose congested areas and find a solution for them, or to predict the traffic situation to avoid occurring traffic jams. There are several methods for representing transportation network data. Some of them are linear such as flow maps. A flow map is a traditional linear method which is capable to show the traffic changes by using different line widths and sometimes varying colours, while their geometry is represented schematically or geographically correct. Other methods are able to show changes of a phenomenon, such as isopleth maps. If an isopleth map is designed based on traffic speed, this map is able to show different congested regions of a transportation network. On the other side, there are new methods for representing transportation network data such as diagram maps. Diagram maps use computational methods to facilitate analysing transportation network data such as a flow diagram map, mosaic map and tree map. For example, in a flow diagram map, speed diagrams are used for illustrating traffic data for specific parts of the transportation network. But, the important issue is, which method is the most usable for representing transportation network data. To measure the usability, the effectiveness, efficiency and satisfaction of each map should be evaluated. In this research the most suitable candidates of linear representations and diagram maps for representing transportation network data (congested regions) are selected based on their characteristics, potentials, advantages and disadvantages. These candidate are designed and implemented on Enschede, the Netherlands as study area and their usability are tested by 21 participants. The usability test results are evaluated generally and specifically (based on spatial and temporal reading levels). The results showed that flow map was usable for intermediate and elementary spatial and temporal reading levels, while the flow diagram map (diagram map) was the most usable in overall spatial and temporal reading level. At the end, This research propose some recommendations for map designers based on the usability test results, problems which are diagnosed in usability test, participants suggestions and challenges which are occurred in design phase. i

5 Acknowledgements First of all, I would like to thank the Almighty God because of his endless kindnesses during the thesis procedure. Without Him I was not able to conclude this thesis. I would like to express gratitude to my first supervisor Dr. Connie Blok for her guidance throughout my research process. Her responsibility about this research was adorable and I will never forget her supports in all stages of this work. I would like to thank my second supervisor Dr. Otto Huisman for his helps and comments during this work. Also, special thanks to my advisor Mrs. Qiuju Zhang for her infinite assistances, I will never forget her cooperation for inviting participants to the usability test and her advices in the design phase. I would also like to convey numerous thanks to Dr. Van Elzakker for his advices and assistance in the usability test and his cooperation as being participant in the pilot test. I want to thank course coordinator Mr. Gerrit Huurneman because of his sincerely cooperation during this research process. He prepared a suitable environment with all essential tools for learning and students like me can use these facilities to do research and achieve their goals. I owe many thanks to programme director Dr. Vosooghi because of his supports and guidance, before and during this research. Also, this research project would not have been possible without the support of the PHD students who participated in usability test. Thousands thanks for your cooperation. I want to thank my friends; they helped me to forget loneliness and made me happy by their supports. At the end, I have this opportunity to express my gratitude to my family, my father and my mother, because of their eternal support during these months. They always gave me emotional support during difficult times and released me from disappointing ideas. I hope this work be a good response to their kindnesses. ii

6 Table of contents 1. Introduction Motivation and problem statement Research identification Main objective Sub objectives Research questions Methodology Structure of the thesis Thematic maps for network data Introduction Literature review User requirements, case study and data User requirements Case study and Data Characteristics of potentially suitable thematic maps Isopleth map: Flow map: Flow map (schematic) Flow diagram map Mosaic map Tree map Selection of map types Assumptions Comparison of the characteristics of candidate maps Conclusion Design and implementation Introduction Software ArcGIS Adobe Illustrator...28 iii

7 Adobe Flash Data processing Design and Implementation Flow map Isopleth map Flow diagram map Conclusion Usability test and results Introduction Usability: What is the usability? What is usability testing? Goals of usability testing Usability testing methods Selecting the usability methods Deciding who the user should be Design of the usability test Questionnaire: Observing and think aloud Test plan Preparing the test Laboratory Check list (test structure) Pilot test Usability test analys and results Criteria Data organization Results on general goals Results on specific goals Disscussion Summary Conclusions and recommendations Conclusions Recommendation for further research Appendices iv

8 List of figures Figure 1: Left the metro map of Amsterdam is shown, right the flow map of human migration from California from 1995 till 2000 is shown (Tobler, 2004)... 2 Figure 2:Left the Tokyo metro is shown ( 2010) and it can be seen that it is more complex than the Amsterdam metro. Right, complexity of a flow map of migration in the whole USA is shown (Tobler, 2004)... 2 Figure 3: Treemaps of 42.2 million vehicles activities in 98 km² of London. Traffic volumes (size) and average speed (colour, km/h) are shown based on data hierarchy from left to right: vehicle types, hours of the day and days of the week(slingsby, et al., 2008)... 2 Figure 4: the flow diagram map of Milan... 3 Figure 5: A speed profile which exhibit the speed value in every 5 minute Figure 6: 59 speed profiles for Enschede Figure 7: The red roads contain data and black roads do not contain data Figure 8 : Total combined truck flows from Texas to other states ("Texas Total Combined Truck Flows," 1998) Figure 9: Tobler s computer generated flow map of migration from California from Figure 10: Flow diagram map of Milan (Andrienko & Andrienko, 2008) Figure 11: Mosaic map of Milan (Andrienko & Andrienko, 2008) Figure 12: Tree maps of 42.2 million vehicles activities in 98 km² of London. Traffic volumes (size) and average speed (colour, km/h) are shown based on data hierarchy from left to right. Vehicle types, hours of the day and day of the week. (Slingsby, et al., 2008) Figure 13: Geographically correct roads (blue) and schematic roads (red) are overlapping to show their differences Figure 14: proposed colours for 5 classes by Colorbrewer.org Figure 15: : different thickness and colours are assigned to lines representing congestion classes: class 1 has 4 mm, class 2 has 3mm, class 3 has 2 mm and class 4 and class 5 have 1 mm thickness. Colours proposed by Colorbrewer are assigned to the 5 classes Figure 16: figure (a) shows the quality of exported map from ArcGIS and figure (b) depicts the quality of exported map from Adobe Illustrator Figure 17: Traffic changes from 6:30 to 8:00 a.m. with 30 minutes interval from picture 1 to picture Figure 18: speeds values are classified as same as the flow map classification and also the colours are assigned to these classes are the same colours which are used in flow map of Enschede Figure 19: picture (a) and picture (b) show the isopleth maps which are interpolated in order by IDW and Kriging method and picture (c) shows the isopleth map which is interpolated by Natural neighbor method Figure 20: Contour lines of isopleth map of Enschede at 16: Figure 21: Traffic changes from 7:00 to 8:30 with 30 minutes interval at morning from picture 1 to picture Figure 22: Example of a speed diagram which is exported from Excel the ArcGIS layout page Figure 23: flow diagram map of Enschede Figure 24: the test environment vi

9 Figure 25: Table designed to encompass all data about each participant such as correctness, face reactions (feeling), time and their comments of each tasks Figure 26: the effectiveness of the flow map (a) shows that 88.09% of the participants did the tasks correctly and the Isopleth map (b) and the Diagram map (c) are placed on the second and third place by 85.72% and 70.24% of correct answers Figure 27: The general comparison of effectiveness of Flow map, Isopleth map and Diagram map Figure 28: The average time for doing tasks in the Flow map, Isopleth map and Diagram map Figure 29: The general comparison of efficiency between Flow map, Isopleth map and Diagram map Figure 30: the satisfaction of flow map (a) shows that 86.90% of the participants were satisfied about the tasks and the Isopleth map (b) and Diagram map (c) are placed on the second and third place by 84.52% and 82.15% of satisfaction Figure 31: The general comparison of satisfaction between Flow map, Isopleth map and Diagram map Figure 32: averages of correctness for each combination of spatial and temporal reading levels Figure 33: averages of time for doing each task relate to specific combination of spatial and temporal reading levels Figure 34: comparison of correctness for specific combination of spatial and temporal reading levels vii

10 List of tables Table 1: spatial and temporal levels of reading defined by Koussoulakou & Kraak (1992) Table 2: Three spatial and temporal levels of reading...10 Table 3: Isopleth map characteristics...16 Table 4: Flow map realistic characteristics...17 Table 5: Flow map with schematic lines...18 Table 6: Flow diagram characteristics...19 Table 7: Mosaic map characteristics...20 Table 8: Treemap characteristics...21 Table 9: the comparison between three linear representation candidates according to user requirements, map characteristics and research assumptions...23 Table 10: the comparison between three diagram representation candidates according to user requirements, map characteristics and research assumptions...24 Table 11: Overall comparison between linear candidate methods...25 Table 12: Overall comparison between diagram candidate representations...26 Table 13: selected candidates for linear representations and diagram maps...27 Table 14: General and specific goals of usability testing...42 Table 15: the check list which is used in this research as usability test structure...47 Table 16: summary of general comparison between Flow map, Isopleth map and Diagram map...52 Table 17: averages of correctness for specific combinations of spatial and temporal reading levels; best results are shown in green...53 Table 18: averages of completion time for doing each task relate to a specific combination of spatial and temporal reading levels...54 Table 19: comparison of correctness for specific combination of spatial and temporal reading levels.56 Table 20: The most usable map for each 6 combinations of spatial-temporal reading levels...57 ix

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12 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data 1. Introduction 1.1. Motivation and problem statement Nowadays, transportation networks play an important role in human life. Due to growing urban areas and increasing communication ways such as roads, railroads and subways, transportation networks have become larger and more complex than before. Transport organization managers and decision makers use data and visualizations related to transportation networks, to analyze and manage the transportation system. Effective visualizations of data on transportation networks can help them diagnose transportation networks problems such as traffic jams and find solutions. Usable network representation methods should create successfully communicates to a diverse audience for a variety of purposes. Representation methods should be usable to help users to achieve their goals with effectiveness, efficiency and satisfaction in their usage context (Jokela, Iivari, Matero, & Karukka, 2003) and should be able to meet some or all of the user requirements such as: displaying coincident point and line events in transportation networks, maintaining network topology, displaying multiple event attributes or associating data with time (Avelar & Hurni, 2006). One of the traditional methods for representing transportation network is linear representations. Linear representations illustrate the connections between points as routes, schematically or realistically. This method can also demonstrate distances or show the relation between points. In this method transportation features like bridges, stations, intersections etc., can be visualized well and the features and events (e.g. car accidents) have their own unique positions along each route. Linear representations are capable to demonstrate movement data such as human migration, schematically or realistic (Avelar & Hurni, 2006; Phan, Xiao, Yeh, Hanrahan, & Winograd, 2005) with or without a transparent network layer. In Figure 1 two different types of linear representation are shown. But representing large amounts of data such as routes, features and events causes overlapping problems and makes linear maps complex and inefficient (Kennedy, 1999). It can be seen in Figure 2 that how massive data sets make linear maps complex. On the other side diagram maps are developed for representing transportation network data. These new methods are computational and suitable for analysing data in huge data sets. For example, Tree maps display hundreds of subsets from large multivariate spatio-temporal data sets simultaneously and allow analysts to find patterns and structures of data. Identifying these patterns and structures can help decision makers to manage the transportation networks and deal with network problems (Andrienko & Andrienko, 2008; Wood & Dykes, 2008) In Figure 3 the tree maps of transportation network data of a region in London is shown. Unfortunately tree maps are limited in some aspects. For example, it is difficult to exhibit linking between nodes and colour can be used only for depicting values of leaf nodes (Slingsby, Dykes, & Wood, 2008). 1

13 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Figure 1: Left the metro map of Amsterdam is shown, right the flow map of human migration from California from 1995 till 2000 is shown (Tobler, 2004) Figure 2:Left the Tokyo metro is shown ( 2010) and it can be seen that it is more complex than the Amsterdam metro. Right, complexity of a flow map of migration in the whole USA is shown (Tobler, 2004) Figure 3: Treemaps of 42.2 million vehicles activities in 98 km² of London. Traffic volumes (size) and average speed (colour, km/h) are shown based on data hierarchy from left to right: vehicle types, hours of the day and days of the week (Slingsby, et al., 2008) 2

14 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Existing treemaps layout algorithms suffer to some extent from poor or inconsistent mappings between data order and visual ordering in their representation, reducing their cognitive plausibility (Wood & Dykes, 2008, p. 1348). Andrienko & Andrienko (2008) proposed flow diagram map and mosaic diagram map to illustrate transportation network data (e.g. traffic speed) by means of diagrams instead of lines. Figure 4 shows a flow diagram map of Milan. In this figure traffic regions are visible by the diagrams which have smaller speed value than the others but still showing linking between nodes are not suitable. Figure 4: the flow diagram map of Milan The sole analysis and sole visualization are not efficient enough to access data patterns in complex data sets (Keim, Mansmann, Oelke, & Ziegler, 2008). Instead, the synergy between human perception and cognition and computational ability, should facilitate the detection of data patterns in massive collections of data (Andrienko, et al., 2007; Kraak & van de Vlag, 2006). Linear representations and diagram maps are capable to represent transportation networks, but in different representation contexts, with different applications. So, the main problem of this research is to investigate potentials, advantages, disadvantages and usability of both linear representations and diagram maps for representing transportation network data for transport organization planners/decision makers. Evaluating linear maps and diagram maps and comparing their usability would add new results on suggestions for correctly selecting suitable representation methods and effectively representing data on transport networks, and therefore enable the transport organization planners/decision makers to understand massive and complex transport network data. 3

15 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data 1.2. Research identification Main objective To analyse and evaluate the usability of linear representations and diagram maps for representing transport network data and to generate recommendations for the designers of such maps that aim at support transport organization planners/decision makers in their tasks Sub objectives a) To investigate potentials of linear representations and diagram maps to represent transport network data. b) To decide on the most potential methods for evaluation. c) To design linear representations and diagram maps for planners/ decision makers who deal with transportation issues. d) To evaluate the usability of linear representations and diagram maps. e) To achieve reliable recommendations for designers Research questions 1. What are the characteristics and potentials of linear representations and diagram maps for transport network data? 2. What are the user s requirements and tasks related to transportation network visualization? 3. Which methods and map types are the best candidates for representing transportation network data in linear representation and diagram maps? 4. What information and materials are available for designing the maps? 5. How should linear maps and diagram maps be designed and evaluated? 6. How can usability of linear representations and diagram maps be measured? 7. What are the recommendations about designing linear and diagram maps? 1.3. Methodology 1) Literature study: Literature study is the first phase of this research and includes main research concepts. Literature study is about linear representations and diagram maps representations characteristics, potentials, advantages and disadvantages. Research questions 1, 2 and partly 3 will be answered in this level. The literature study continues as input for the other faces below. 2) Theoretical framework: In the second phase, a theoretical model will be designed based on information gained from the literature study. In this phase appropriate candidate maps for representing transportation network data in linear representations and diagram maps, will be proposed for evaluation. Question 3 will be answered in this level. 3) Design maps: In 3 rd phase the most suitable candidates of each representation type will be designed based on speed profiles (which are available) and information from literature study using the case study. For designing and implementing appropriate software will be needed. Questions 4 and 5 will be answered in this level. 4

16 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data 4) Evaluation: In 4 th stage, layouts and results of the designed maps will be tested, analyzed and evaluated based on their usability. The results of each map will be compared to draw conclusions about their advantages, disadvantages and potentials. Question 6 will be answered in this level. 5) Development of recommendations: In the last part, recommendations will be proposed to design maps that support decision makers with usable visualizations (linear representations and diagram maps) of transport network data. Question 7 will be answered in this level Structure of the thesis 1) Chapter 1 is about an introduction about motivation and problem statement and objective and sub-objectives of this research. 2) Chapter 2 contains literature review (related works) and evaluation of linear representations and diagram maps. In this chapter most suitable candidates for representing transportation network data are selected based on user requirements. 3) Chapter 3 is about data processing, designing and implementing candidate maps which are selected in chapter 2 on case study (Enschede, the Netherlands). 4) Chapter 4 is about measuring the usability of designed maps. In this chapter the goals and methods of usability are explained and the usability test results are evaluated. 5) Chapter 5 contains a summary of the research and the recommendations of designs. In this chapter whole the procedure is explained briefly and based on usability test results some recommendations are mentioned. 5

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18 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data 2. Thematic maps for network data 2.1. Introduction In this chapter, a theoretical framework will be designed based on information achieved from the literature study phase on potentially suitable maps and on user requirements. The survey aims at obtaining information about various candidate maps based on linear and diagram representation methods to find the most suitable candidates for each method for representing transportation network data. To find the most suitable candidates of each method, a comprehensive comparison would be necessary. This comparison will be based on context of use, users, user requirements, characteristics of the data and the map types. This chapter is followed by a literature review on linear representation and diagram maps (2.2.), surveying of user requirement, case study and data (2.3.), evaluation of characteristics of suitable candidate maps (2.4.) and selecting the most suitable candidates for each map type (2.5) Literature review A transportation network is a geographical object with a spatial dimension (nodes location), a metric dimension (nodes and edges attributes) and a topological dimension (the relationships between these nodes through edges). (Mermet & Ruas, 2010, p. 1) Users (transportation planners/decision makers) needs understandable maps and interfaces with maps to achieve their answers about when, what and where as basic requirements. The components of transportation network data can be represented in different ways. Transportation networks contain data about movement objects in space and time, so an appropriate visualization method should demonstrate spatio-temporal information in a suitable environment. Various representation methods (thematic map types) that can somehow handle spatio-temporal aspects have been proposed till now for transportation network data, but the question is which method is most suitable. Bertin (1983) classified the structure of network maps into five groups (rectilinear, circular, irregular arrangement, regular arrangement and perspective drawing). Also, Dent (1999, pp )explained network representations and proposed flow maps for representing movement data in export, migration or transportation networks. He also classified flow maps into three groups (radial, distributive and network), while Slocum (2009, pp ) classified flow maps into five groups (he added continuous and telecommunication flow maps to Dent s three classes). Ruggles & Armstrong (1997) complained about the lack of a complete framework for representing transportation network data and pointed at flow maps as a method for representing data in transportation network. 7

19 But showing large amounts of data such as routes, features and events makes linear maps complex and inefficient (Kennedy, 1999).Tobler (1987) focused on important movements in flow maps design and eliminated under average values of migrations to emphasis on important migration movements by generating the schematic flow map. Phan and Ling et al.(2005) introduced another method to design flow maps by reducing visual clutter and merging edges. Linear representations in schematic maps are used for many decades due to their legibility and understandable symbolization. For instance, Henry C. Beck designed the London underground network map in 1933 to help people to travel easy and safe (Jenny, 2006). Avelar and Hurni (2006) evaluated schematic representation effects of public transportation network data on travellers by sufficient symbolization and decreasing details. They suggested automatic schematization for designing schematic maps. They also surveyed the effects of schematic maps on users (travellers) in a Zurich experiment (2001). Agrawala and Stolte (2001) used a system for designing and rendering to improve usability of route maps and Jenny (2006) used MapAnalyst software to measure accuracy and distortion of schematic maps. All of the methods that are mentioned above are basically linear, which means these methods use lines and zones as symbols for showing the connection between nodes and depicting transportation network data such as traffic congestions. For example, Flow maps use flow lines for showing movement data between nodes and can illustrate different volume of movement data between nodes by changing the width of lines. On the other hand, for large and complex multivariate data sets, other visualization methods are available which utilize diagrams instead of lines for depicting data of transportation networks. For exploring and analysing the massive data collection, visualization alone may be not enough and there is a need to combine visualization methods with computational analysis methods (Andrienko & Andrienko, 2007). Andrienko & Andrienko (2008) proposed various spatio-temporal methods such as mosaic diagram and flow diagram. On the other side, Wood & Dykes (2008) surveyed treemaps which have been proposed by Shneiderman (1992) for the first time and Slingsby et al (2008) examined treemaps on a part of the London transportation network. It is true that finding suitable candidate for representing transportation network data among many potential methods is hard, but the method(s) which can cope with important user requirements would be considered as a candidate of transportation visualisation method User requirements, case study and data User requirements A map type is not applicable for every purpose. If someone decides to travel by car, it is obvious that cycling map or metro transportation map is not useful for him/her. Due to variation of users and use context, map designers are forced to design based on context of use and user requirements as the start point of design in a user-centred design approach. 8

20 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Van Elzakker& Wealands (2007) have mentioned three basic principles for user-centred design: 1) An early focus on understanding the users and the context of use. 2) Empirical evaluation of design products by representative users. 3) An iterative cycle of design production, evaluation and redesign. (Gould & Lewis, 1985; Jokela, et al., 2003) Due to these principles, recognizing the user is the first step for achieving user-centred design. The answer to simple question who is the user (Nielsen, 1992), helps to diagnose users goals and associated the tasks and leads to (geospatial) requirements for map design. In cartographic visualization, the question: Who is the user? also has a long tradition. This research considers as users traffic managers and planners who want to analyze where and when congestion levels along roads exist, to decide on measures to relieve congestion. They analyze the transportation networks data to find problems and try to solve them to improve system mobility along the transportation network. Understanding a complex data set such as transportation network data is not simple and analysts should survey the correlations in the data set (Guo, Gahegan, MacEachren, & Zhou, 2005). Visualization techniques are able to facilitate data analysis for analysts by depicting spatio-temporal data and offering support to analyze data dynamically(kraak & van de Vlag, 2006). Users are eager to achieve important information from huge transportation network data sets. Traffic managers and planners aim to detect the pattern of congested areas, to find traffic regions and critical time intervals (rush hours) of traffic to avoid traffic jams or find a solution for those areas and periods of time. They should diagnose where and when the congestions would be occurred. Peuquet (1994) classified spatio-temporal questions to three main groups : Where (e.g.: the region of congestions) When (e.g.: rush hours) What (e.g.: what is the value of average speed) Bertin (1983) defined three levels of reading for spatial questions of users. These levels of reading are elementary (for one location or element), intermediate (some related elements or a small area) and overall (over all elements) and Koussoulakou& Kraak (1992) defined three temporal levels of reading in Elementary (a moment of time), intermediate ( time intervals or a period of time) and overall (whole time). Based on spatial and temporal reading levels, the requirements of traffic managers and planners could be finding answers to different combinations of questions at spatial and temporal reading levels as classified below: Spatially: What is the situation of traffic in specific part of transportation network? What is the situation of traffic in some parts of transportation network? What is the situation of traffic in whole transportation network? Temporal: What is the traffic situation at specific time? 9

21 What is the traffic situation in specific time intervals? What is the traffic situation over the whole time? Table 1 illustrates spatial and temporal levels of reading, defined by Koussoulakou & Kraak (1992). In this table the elementary and intermediate levels of readings are combined as local level. By separating local level to elementary and intermediate level the table would be changed as shown in Table 2. Table 1: spatial and temporal levels of reading defined by Koussoulakou & Kraak (1992). Elementary particular road particular moment particular road Period of time particular road Whole time Spatial Intermediate Particular roads particular moment Particular roads Period of time Particular roads Whole time overall Whole Network particular moment Whole Network Period of time Whole Network Whole time Elementary Intermediate Overall Temporal Table 2: Three spatial and temporal levels of reading In this research, elementary, intermediate and overall temporal reading level tasks and intermediate and overall spatial reading level tasks are considered. Elementary spatial reading level is omitted from the tasks because it needs zooming and filtering methods which are not covered by this research. Appropriate representation methods should support most of these requirements to be useful for users. In the next section, the most suitable candidate methods will be evaluated. 10

22 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Case study and Data The case study of this research is Enschede, a city with inhabitants in the east of the Netherlands. The available data set is average speed profiles of Enschede. A speed profile represents speed behaviour along transportation elements or a set of transportation elements sharing the same speed behaviour in every five-minute over a 24-hour period. A speed profile is shown in Figure 5 and all 59 speed profiles for Enschede are shown in Figure 6. Each transportation element has a specific speed profile assigned per day of the week. The time intervals are calculated after midnight (00:00) (TeleAtlas, 2010). Figure 5: A speed profile which exhibit the speed value in every 5 minute Figure 6: 59 speed profiles for Enschede 11

23 To achieve data about the Enschede, the region of Enschede is clipped in ArcGIS and separated from a bigger set and all data about Enschede is saved as an independent layer in ArcGIS. Then the projection system of Enschede s layer is matched to the Netherlands projection (RD_NEW) The available data set does not contain recorded speed for all roads of Enschede. Based on the available data set, 8562 segments are identified but just 2636 segments contain speed profiles and the others do not contain speed value. Figure 7shows the roads of Enschede which speed is recorded and speed profiles are available for them. Figure 7: The red roads contain data and black roads do not contain data 12

24 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data 2.4. Characteristics of potentially suitable thematic maps As mentioned before, an appropriate representation method(s) should support most of user requirements to be useful for users. According to achieved information from literature study about maps abilities for representing congested areas, three candidate maps are selected for each representation method (linear and diagram maps). Flow map realistic and flow map schematic are considered as candidates for linear visual representation. But there are still some methods which are not considered in network representation classifications such as the isolines maps and isopleth maps. They can represent network data but in a different context. Isolines are commonly used for showing the earth elevation and show dominant points (high elevation spots) and slopes (MacEachren & Davidson, 1987; Montello & Gray, 2005) while isopleth maps are utilized for depicting different zones of (classified) temperature, pollution, population etc. So, the isopleth map would be a good candidate for visualizing information about congestions. For instance, isopleth maps can illustrate the congested areas or segments with relatively low, intermediate and high percentages of free flow speed by colourful regions and contour lines. But, isolines just use lines for showing different regions and would not be as good candidate for representing congested regions. Figure 8 illustrates an example for flow map geographically correct. In this figure the total combined truck flows from Texas to other states of the United States are shown. Figure 9 is an example for flow maps schematic and depicts Tobler s computer generated flow map of migration from California from (Tobler, 2004). Figure 8 : Total combined truck flows from Texas to other states ("Texas Total Combined Truck Flows," 1998) 13

25 Figure 9: Tobler s computer generated flow map of migration from California from Flow diagram maps, mosaic maps and tree maps are selected as candidates for diagram representing method of transportation network data. Figure 10 illustrates flow diagram map of Milan which is designed by Andrienko & Andrienko (2008), Figure 11 shows a mosaic map of Milan as an example of mosaic map which is made by Andrienko & Andrienko (2008) and Figure 12 exhibits an instance of a tree map representation which is generated by Slingsby et al. (2008) to show the traffic in a region of London. Figure 10: Flow diagram map of Milan (Andrienko & Andrienko, 2008) 14

26 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Figure 11: Mosaic map of Milan (Andrienko & Andrienko, 2008) Figure 12: Tree maps of 42.2 million vehicles activities in 98 km² of London. Traffic volumes (size) and average speed (colour, km/h) are shown based on data hierarchy from left to right. Vehicle types, hours of the day and day of the week (Slingsby, et al., 2008) The characteristics and variations of the pre-selected representation methods are analyzed and summarized in some tables to facilitate the comparison between them. Table 3, Table 4 and Table 5 illustrate, in order, characteristics of the isopleth map, flow map realistic and schematic flow map. Also Table 6, Table 7 and Table 8 demonstrate, in order, characteristics of the flow diagram map, mosaic map and tree map. 15

27 Isopleth map: Isopleth map An isopleth map consists of isolines (contour lines) which connect the points with similar values to display the distribution and gradient changes of a phenomenon. Isopleths also use colour/colour value between the isolines to show regions of classified values (Slocum, 2009). Isopleth maps are being used for showing temperatures, landslide, elevations or population densities (Bulut, Boynukalin, Tarhan, & Ataoglu, 2000; DeGraff & Canuti, 1988; Fremlin & Robinson, 1998). Data that can be represented Nodes Lines Attributes Time Junctions and nodes Roads or segments of network and contour lines (the lines contain points with equal values and can demonstrate the specific area which includes a group of values) Volume of movement in various areas. continuously Possible: linear, partly cyclic Map enables Answers to where, what, when questions Display of connectivity Spatial reading levels Temporal reading levels Yes (3x) Yes intermediate, overall Elementary; intermediate and overall if animated Representation Nodes geometry Lines geometry Attributes Time Geographically correct Geographically correct (Classified) speed is represented by specific regions.. Static (for one moment) or dynamic by animating Table 3: Isopleth map characteristics 16

28 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Flow map: Flow map (geographically correct) Flow map represents quantitative attributes of flow along transportation routes by lines of proportional widths. Direction may or may not be included. To show movement object between places, quantitative or qualitative, flow map is appropriate (Dent, 1999; Slocum, 2009). Data that can be represented Nodes Lines Attributes Time Junctions and nodes Roads or segments of networks Volume of movement between nodes: discrete Possible: linear, partly cyclic Map enables Answers to where, what, when questions Display of connectivity Spatial reading levels Temporal reading levels Yes (3x) Yes Elementary, intermediate, overall Elementary; intermediate and overall if animated Representation Nodes geometry Lines geometry Geographically correct Geographically correct Attributes (Classified) volumes are represented by the width of lines; If multivariate data: colour can be added to the lines Time Static (for one moment) or dynamic by animating Table 4: Flow map realistic characteristics 17

29 Flow map (schematic) Another type of flow map which has geographically correct nodes and schematic lines. Flow map (schematic) Flow map represents quantitative attributes of flow along transportation routes by lines of proportional widths. Direction may or may not be included. Data that can be represented Nodes Lines Attributes Time Junctions and nodes Roads or segments of networks Volume of movement between nodes: discrete Possible: linear, partly cyclic Map enables Answers to where, what, when questions Display of connectivity Spatial reading levels Temporal reading levels Yes (3x) Yes Elementary, intermediate, overall Elementary; intermediate and overall if animated Representation Nodes geometry Lines geometry Geographically correct Geographically incorrect (schematic) Attributes (Classified) volumes are represented by the width of lines; If multivariate data: colour can be added to the lines Time Static (for one moment) or dynamic by animating Table 5: Flow map with schematic lines 18

30 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Flow diagram map Flow diagram map Flow diagram maps represent data by means of diagrams. These static maps, illustrate data for specific period of time for a particular region of a study area. The differences between regions can be inferred by comparing their diagrams. Andrienko & Andrienko (2008) used this map to show the congested area in Milan. Data that can be represented Nodes Lines Attributes Time Junctions and nodes Roads or segments of networks Volume of movement between nodes in a specific region. discrete Possible: linear Map enables Answers to where, what, when questions Display of connectivity Spatial reading levels Temporal reading levels Yes Yes Intermediate, Overall Elementary; intermediate and overall Representation Nodes geometry Lines geometry Attributes Geographically correct Geographically correct Speed and time are represented via diagrams. Time Static Table 6: Flow diagram characteristics 19

31 Mosaic map Mosaic map Mosaic maps are another type of diagram maps. Mosaic maps are proposed by Andrienko & Andrienko (2008) to show the congested areas in Milan. In this map, each mosaic contains 7 x 24 parts (each mosaic illustrates seven days of a week and 24 hours for each day) and each part shows the value of speed by specific colour (from red as high congestion to green as a little congestion). As you can see in Figure 11 the most congested areas are demonstrated by red, and the other areas are somehow green which means there are less traffic. Data that can be represented Nodes Lines Attributes Time Junctions and nodes Roads or segments of networks Speed of movement between nodes in a specific region. discrete linear Map enables Answers to where, what, when questions Display of connectivity Spatial reading levels Temporal reading levels Yes Yes Overall Elementary; intermediate and overall Representation Nodes geometry Lines geometry Attributes Time Geographically correct Geographically correct (Classified) speed is represented via diagrams. Static Table 7: Mosaic map characteristics 20

32 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Tree map Tree map Two-dimensional (2-d) space-filling approach in which each node is a rectangle whose area is proportional to some attribute such as node size. (Shneiderman, 1992, p. 92) Information can be represented by the size of nodes, the colour of leaf nodes, the spatial order (or more generally, layout) of nodes and a label for each node. (Slingsby, et al., 2008, p. 213) Treemaps are capable to illustrate attributes of data base with nodes. Each node is a rectangle that can represent data attributes by variation in size, colour or label of each node. Data that can be represented Nodes Lines Attributes Time Are represented by leafs of the tree Cannot be represented Type and volume of movement between nodes in a specific region. Nominal, ordinal or ratio level; discrete linear Map enables Answers to where, what, when questions Display of connectivity Spatial reading levels Temporal reading levels Yes No intermediate and overall elementary or intermediate Representation Nodes geometry Lines geometry Attributes Time Cannot be represented Cannot be represented (Classified) speed or volume is represented by size of nodes, colour of nodes and labels Static Table 8: Treemap characteristics 21

33 2.5. Selection of map types In this section, the in theory most suitable maps for each representation method (diagram and linear) are selected. In this research, some assumptions are defined about map characteristics that take user requirements into account and that are important for the execution of tasks with network data. According to these assumptions, the comparison between methods is executed Assumptions These assumptions are defined based on user requirements and map characteristics to facilitate comparison between methods: Nodes: nodes are the start and end point of each segment or intersection and should be represented geographically correct to illustrate the location of traffic and be comparable with other maps. Lines: lines are roads and can be represented geographically correct or incorrect (schematic) Attributes: the suitable candidate map should demonstrate the congested areas in transportation network of Enschede, speed value and time. Time: the suitable candidate should illustrate (changes) in congestion levels from 6:00 am till 8:00 pm. Display of connectivity: shows the relation between parts of the network and facilitate diagnosing the location of congested parts of the transportation network. A suitable method should depict the connectivity of the network. Spatial reading levels: intermediate and overall need to be supplemented. Temporal reading levels: elementary, intermediate and overall, because the candidate maps should illustrate time for users in specific moment or even in time interval. Comparability: the selected maps should cope with same tasks based on combinations of spatiotemporal reading levels and should represent same data Comparison of the characteristics of candidate maps According to user requirements, map characteristics and research assumptions, the comparison between maps is executed and the results are shown in two tables. Table 9 and Table 10 show the candidate maps of linear representations and diagram maps and their capability for representing transportation network data. Based on candidate maps characteristics and defined assumptions for selecting maps, the comparison of candidate maps are executed and their advantages and disadvantages are shown in Table 11(for linear representations) and Table 12 (for diagram maps). 22

34 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Map type Map tasks Showing congested areas in spatial intermediate and temporal elementary reading levels Showing congested areas in spatial intermediate and temporal intermediate reading levels Showing congested areas in spatial intermediate and temporal overall reading levels Showing congested areas in spatial overall and elementary temporal reading levels Showing congested areas in spatial overall and temporal intermediate reading levels Showing congested areas in spatial overall and temporal overall reading levels Flow map realistic Flow map schematic Isopleth map possible possible possible possible possible possible possible possible possible possible possible possible possible possible possible possible possible possible Speed values possible possible possible Time (from 6:00 to 20:00) possible possible possible Display connectivity of lines possible possible possible Display nodes (geographically correct) possible possible possible Table 9: the comparison between three linear representation candidates according to user requirements, map characteristics and research assumptions 23

35 Map type Map tasks Showing congested areas in spatial intermediate and temporal elementary reading levels Showing congested areas in spatial intermediate and temporal intermediate reading levels Showing congested areas in spatial intermediate and temporal overall reading levels Showing congested areas in spatial overall and elementary temporal reading levels Showing congested areas in spatial overall and temporal intermediate reading levels Showing congested areas in spatial overall and temporal overall reading levels Flow diagram map Mosaic map Tree map possible possible possible possible possible possible possible possible possible possible possible possible possible possible possible possible possible possible Speed values possible possible possible Time (from 6:00 to 20:00) possible possible possible Display connectivity of lines possible possible possible Display nodes (geographically correct) possible possible possible Table 10: the comparison between three diagram representation candidates according to user requirements, map characteristics and research assumptions 24

36 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data MAP TYPE 1 Flow map: nodes and lines geographically correct (realistic) ADVANTAGES DISADVANTAGES Advantages: It can illustrate connection between points; Three spatial reading levels are possible (just intermediate and overall reading level for spatial are necessary). It can demonstrate congestions in flow lines by using size variation in line widths and illustrating the values of traffic by different colours. Disadvantage: By increasing details it becomes more complex. 2 Isopleth map Advantages: It can illustrate congested areas by contour lines and assign various colours to classified congested zones. Congestions can be shown as congested region with a specific colour/value. Disadvantage: Isopleth map is used for distribution of continuous phenomena, so it cannot show high sudden changes in data set and this may reduce the accuracy of map. 3 Flow map, Nodes geographically Correct (realistic), Lines not geographically correct (schematic) Advantages: Same as for flow map realistic. Disadvantage: Illustrate the networks elements schematically and it is similar to flow map realistic. Table 11: Overall comparison between linear candidate methods It can be inferred from Table 9 and Table 11 that the flow maps (realistic and schematic) seems to be appropriate maps for illustrating transportation network data, but they are very similar to each other. Figure 13 depicts the differences between geographically correct and schematic lines of the transportation network of Enschede. a b Figure 13: Geographically correct roads (blue) and schematic roads (red) are overlapping to show their differences 25

37 To design schematic lines with fix points, the Douglas-Peucker algorithm is used. The Douglas algorithm is one of the options provided by ArcGIS for generalizing lines. It can be seen that the differences between these two maps are negligible, but the geographically correct map is more suitable because it is comparable with the other candidates and shows the realistic connectivity of the transportation network while schematic representations shows the schematic lines. The other candidate is isopleth map. Table 11shows that the isopleth map has a disadvantage for illustrating sudden changes but it can be understood from Table 9, that, isopleth map can cope with user tasks. Therefore, in this research both flow map and isopleth map are considered theoretically suitable and these methods are selected for the evaluation of transportation network maps. MAP TYPE ADVANTAGES DISADVANTAGES 1 Flow diagram map Advantages: 1. Simple to use for three reading levels in temporal and intermediate and overall reading levels in spatial aspect. 2. No need to animate the map. 3. Illustrate the congestion per hour. 4. The situation of congested regions is understandable and the connectivity of roads is observable. Disadvantage: Showing long time period (a whole week) is not possible. For showing long period of time, high generalization in time would be needed. 2 Mosaic diagram map Advantages: Distinguishable colours for each mosaic facilitate diagnosing the congested areas from other areas. Disadvantages: 1. The changes of congested regions are not understandable 2. Elementary or intermediate temporal reading level for overall spatial reading level cannot be 3 Tree map Advantages: Simple to use for three reading level in temporal and elementary and intermediate reading in spatial. Disadvantage: 1. Cannot depict the changes of traffic in three temporal levels of reading. 2. Elementary or intermediate temporal reading for overall spatial reading level cannot be inferred. 3. Showing connectivity of roads is not possible. Table 12: Overall comparison between diagram candidate representations 26

38 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Also, it can be inferred from Table 10 and Table 12 that the theoretically most suitable candidate of diagram maps for representing transportation network data is flow diagram map. Because this map can cope with user tasks in all temporal reading level and also in intermediate and overall spatial reading level. The other candidate for diagram map is mosaic map (Figure 11) but mosaic map cannot cope with elementary and intermediate temporal reading level tasks. Finding the pattern of traffic for specific time interval in mosaic map is so hard and actually this map is suitable for temporal overall reading level. The last candidate of diagram maps is treemap but it cannot cope with spatial reading levels in a geographic sense, and does not show the connectivity between lines. Table 13shows the selected candidates for linear representations and diagram maps for representing transportation network data. Linear representations Diagram maps Flow map (geographically correct) Isopleth map Flow diagram map Table 13: selected candidates for linear representations and diagram maps 2.6. Conclusion In this chapter, based on information achieved from literature study phase, three candidate maps for linear representation and three candidate maps for diagram maps were identified. The context of use, users and user requirements were considered. According to the user requirements and map characteristics, research assumptions were defined to facilitate the selection of theoretically suitable candidate maps that can be included in the evaluation. Based on research assumptions the comparison between candidate maps was executed and the theoretically most suitable maps for linear representations (flow map and isopleth map) and diagram maps (flow diagram map) were selected for design and implementation on the Enschede transportation network. 27

39 3. Design and implementation 3.1. Introduction Based on research assumptions and the maps characteristics, flow map and isopleth map for linear representation method and flow diagram map for diagram representation method were selected. In this chapter, design and implementation of these maps will be explained and the challenges during their production will be discussed. This chapter contains an evaluation about appropriate computer software for designing map (3.2.), data processing (3.3.) and the design and implementation of selected maps in previous chapter (3.4) Software ArcGIS ArcGIS is a GIS software that can help users to analyse spatial data and produce maps. Also, ArcGIS is capable to process and manage data base. ArcGIS is used in this research to process the data, design and implement traffic maps on case study (Enschede) Adobe Illustrator Adobe illustrator is powerful graphical software that allows users to generate complex graphical designs with many special effects. Adobe illustrator is able to vectorize raster files and to enhance the recognized lines, it is also able to convert files to other formats (ex. AI to JPEG) ( 2010b). In ArcGIS users are able to export their maps directly in AI format. Illustrator is able to reduce the size of the final maps and increase their qualities by vectorizing them. Adobe Illustrator CS5 is used in this research to vectorize the imported map from ArcGIS Adobe Flash Adobe Flash software is a useful platform for generating animation with images and it can facilitate the process of making animation. Users are able to animate exported maps from Adobe Illustrator or ArcGIS and add labels, time or a legend to the animated map ( 2010a). Adobe Flash player CS5 is used in this research to animate exported maps from ArcGIS Data processing The TeleAtlas data set contains 59 speed profiles for road segments of Enschede for seven days of a week, and table with percentages of free flow speeds for each speed profile per 300 second in 24 hours. The profiles are coded from 1 to 59 and the speed of each segment is shown by the code of speed profiles not the value of speed. To achieve the percentage of the free flow speed (FFS) for each profile, a process is executed in ArcGIS. This process is shown below via an example. For estimating the percentage FFS of speed profiles at 8:00 am: 1. The time is calculated from 00:00 at midnight (8:00 = 8 x 60 x 60 = second ) 2. The values for seconds for all 59 profiles in the percentage speed table are selected. 28

40 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data 3. The selected amounts are exported to new table ( 8:00 percentage speeds) 4. The speed profile table and 8:00 percentage speeds are combined to replace the speed profiles by the percentage of FFS at 8:00 in new field in the speed profile table Design and Implementation Flow map The flow map of Enschede aims to illustrate the congested areas and traffic jams from 6:00 till 20:00 for every 30 minutes and also helps users to diagnose the different levels of speed values at different hours of a day in Enschede. For designing flow map of Enschede, the summary of Essential design strategies (Dent, 1999, pp ) for creating flow maps is considered. Borden Dent s Essential design strategies are: 1. Flow lines are highest in intellectual and therefore highest in visual/graphic importance. 2. Smaller flow lines should appear on top of larger flow lines. 3. Arrows are necessary if direction of flow is critical to map meaning 4. Land and water contrasts are essential (if the mapped area contains both). 5. Projection, its centre and aspect, are used to direct readers attention to the flow map pattern important to the map s purpose. 6. All information should be kept simple, including flow line scaling. 7. Legends should be clear and unambiguous, and include units where necessary. Creating effective flow maps through a careful and thoughtful design plan represents one of the more difficult challenges for the map designer. Three aspects of design must be considered: map organization and figure-ground (including the selection of the projection), line symbolization and data scaling, and map legend. (Dent, 1999, p. 226) A flow map shows levels of FFS by assigning different colours to each speed level or uses various thicknesses of lines widths according to their amounts. As first step the speed values should be classified The classification of speed values is executed based on distribution of percentage of free flow speed in Enschede (the minimum value of data set is 44% and the maximum value is 100%) and also based on map purpose to show the congested areas. The percentage of FFS is commonly more than 80% and the amounts should be classified regularly. The other issue for flow map classification is the number of classes. Although considering fewer classes increases the legibility of flow map and users can find out the differences between classes easily, a low number of classes would generalize the speed amounts and users lose information about details. 29

41 On the other side, diagnosing and understanding of a large number of classes and colours would be confusing for users. So, according to data set values the classification of speed values is considered from highly congested to low congestion as shown below: Classification of speed values: 44 %< Class1 < 55% 55% < Class 2 < 65% 65% < Class 3 < 75% 75% < Class 4 < 85% 85% < Class 5 < 100% In the next step, for emphasising congested segments, different lines widths and various colours are assigned to each class. As can be seen in Figure 15, most thickness is assigned to the first class (most congested) and the minimum thicknesses assigned to last class (least congested). Also, to distinguish the classes and make map more legible, various colours are assigned to these classes. Assigning colours to speed classes is very important issue and it directly affects on users satisfaction. If colour schemes are not carefully constructed and applied to the data, the reader may become frustrated, confused, or worse, misled by the map. (Harrower & Brewer, 2003, p. 27) In addition, if A map reader diagnoses the differences between colours in the legend, it does not mean that they can recognize colours on the map (Brewer, 1997). For assigning colour to each class the Colorbrewer system is used (Figure 14). Colorbrewer is an online tool for users to identify the most suitable colour schemes for maps. The system allow users to identify how many data classes they have and also what kind of colour they prefer then system suggests most suitable and distinguishable colour schemes (Harrower & Brewer, 2003). Due to the importance of congested areas in the transportation network, the red colour is assigned to the class 1 (low percentage of FFS) to emphasize this class more than the other classes and somehow warn user about this class. 30

42 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Figure 14: proposed colours for 5 classes by Colorbrewer.org Figure 15: : different thickness and colours are assigned to lines representing congestion classes: class 1 has 4 mm, class 2 has 3mm, class 3 has 2 mm and class 4 and class 5 have 1 mm thickness. Colours proposed by Colorbrewer are assigned to the 5 classes. The flow map of 16:00 is shown in Figure 16 (a) as an example of flow maps of Enschede. For demonstrating light colours such as yellow and light green, 40% gray back ground is used. To increase the quality of maps, the maps are exported from ArcGIS to Adobe illustrator software to vectorize lines of flow map and increase the quality of map. Figure 16 (b) is showing the flow map of 16:00 which is exported by adobe illustrator. 31

43 It can be inferred from the Figure 16 that the quality of Adobe illustrator map is higher than the map that is exported by ArcGIS. a b Figure 16: figure (a) shows the quality of exported map from ArcGIS and figure (b) depicts the quality of exported map from Adobe Illustrator. A flow map illustrates the different speed levels at a specific moment. So, to show a time interval such as 6:00 to 20:00, the flow maps should be animated. In Figure 17 the animation of congestion changes in Enschede between 6:30 and 8:00 is shown. ArcGIS is able to produce animation of different layers, but for producing animation of flow maps, the Adobe Flash player software is used. Adobe Flash player can facilitate making of animation and is also able to make legends and titles for animated maps. Moreover, it is capable to use exported maps from Adobe Illustrator. 32

44 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Figure 17: Traffic changes from 6:30 to 8:00 a.m. with 30 minutes interval from picture 1 to picture

45 Isopleth map Isopleth maps demonstrate the region of each congestion class by various colours and contour lines. The goal is producing the isopleth maps for representing traffic in Enschede and help users to diagnose the different congestion levels from 6:00 till 20:00 for every 30 minutes of a day. To generate an isopleth map and to create the different speed regions and contour lines, a suitable interpolation method is needed. To start interpolation, a point shape file is needed as an input. So, at the first step the roads (linear shape file) of the transportation network are converted to points (point shape file) via convert tool in ArcGIS Spatial Analysis. For selecting the appropriate interpolation method, the context of use, the type of data and accuracy of method should be considered and it should be decided that which technique is the most suitable method for interpolation in specific situation. There are several interpolation methods in ArcGIS software. Based on available data set and the research goal, Inverse distance weighted (IDW), kriging and Natural neighbor are surveyed as interpolation method. IDW method classifies points by weighting them based on their distances to an object. IDW uses inverse-distance function to weight points which means less distance to object has the highest weight and effect and by increasing the distance the weight an effect of points decrease (Slocum, 2009, pp ) Kriging interpolation method is similar to IDW method. It assigns weights according to distance or direction to surrounding measured location values to predict unmeasured locations. But the method for assigning weights algorithm in kriging is more sophisticated than IDW (Slocum, 2009, pp ; webhelp.esri.com, 2010) Natural neighbor method connects close areas with similar values to each other. This method uses average weight and is able to cope with large input point data sets with high point distribution (Sibson, 1981) The IDW, Kriging and Natural neighbor method are selected as method for interpolating. In Figure 19 the results of all three methods for 16:00 are shown. It can be inferred from Figure 19 although, the results of IDW and Kriging are match with flow line map, the shapes of speed regions are look over estimated in some parts. But the map which is interpolated by Natural neighbor interpolation methods looks more reasonable (better shape) and more accurate than IDW and Kriging method so for designing an isopleth map, the natural neighbor interpolation technique is selected. After interpolation, the contour lines are calculated and added to map to show the boundaries of classes. Figure 20 shows the contour lines of isopleth map of Enschede at 16:00. After interpolation, the different speed regions are classified in the same way as the flow map classification and also the colours assigned to these classes are the same colours as used in the flow map. The same classification of speed levels with the same colours would facilitate the comparison between flow map and isopleth map. Figure 18 illustrates the colours which are used for those areas. 34

46 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Figure 18: speeds values are classified as same as the flow map classification and also the colours are assigned to these classes are the same colours which are used in flow map of Enschede a b c Figure 19: picture (a) and picture (b) show the isopleth maps which are interpolated in order by IDW and Kriging method and picture (c) shows the isopleth map which is interpolated by Natural neighbor method 35

47 Figure 20: Contour lines of isopleth map of Enschede at 16:00 The isopleth map illustrates the traffic situation of Enschede in specific moment, therefore, to show whole period of time (from 6:00 till 20:00) isopleth maps should be animated. Like the flow map of Enschede, the isopleth maps are converted to vector files via Adobe Illustrator software and vector maps are animated by Adobe Flash player software. In Figure 21 changes of traffic are shown from 6:30 till 8:00 with 30 minutes intervals. 36

48 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Figure 21: Traffic changes from 7:00 to 8:30 with 30 minutes interval at morning from picture 1 to picture 4 37

49 Flow diagram map To produce flow diagram map, the region of study should be divided to equal parts by means of squares. Each square contains a flow diagram of Free Flow Speed of that region from 6:00 to 20:00. For generating these diagrams, all segments in each square should be selected and the average of speed for each hour (from 6:00 to 20:00) for all segments should be calculated. The flow diagrams should be drawn in external software because in ArcGIS it is not possible to draw diagrams for each part. Common software for drawing diagrams is Microsoft Office Excel. ArcGIS is able to import diagrams from Excel into the layout page. Figure 22 shows an example of a speed diagram which is exported by Excel to the ArcGIS layout page. The X axis shows hours of the day from 6:00 to 20:00 which is marked by grid lines for every three hours to facilitate temporal reading levels and the Y axis shows average of Free Flow Speed for the segments of each part of the diagram map from 70% to 100% (no value was less than 70% in diagram maps parts). Figure 22: Example of a speed diagram which is exported from Excel the ArcGIS layout page. Another important issue is the size of each square. If sizes of squares were too big and encompass a vast area, it would cause high generalisation and understanding the changes of traffic congestions would be difficult. Moreover, if sizes of squares were too small, the map would not cope with elementary and intermediate temporal reading levels tasks efficiency and users would have some trouble with reading time in the map. Also, due to lack of data in some parts of the region of study, the blank squares (no data squares) would happen within the map and reduce the beauty of map. For the flow diagram map of Enschede (Figure 23), a 7x7 grid is used but just the 6x6 in the middle of the map contain diagrams and margin squares are blank due to lack of road segments or data. To illustrate the position of network, the road map of Enschede is overlaid on the diagrams. Flow diagram map is a static map that shows the values from 6:00 to 20:00 in diagrams. 38

50 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Figure 23: flow diagram map of Enschede 3.5. Conclusion In this chapter, via ArcGIS software, the speed profiles are processed and fundamental data for designing of maps are achieved and three selected candidate maps were designed and implemented on study area (Enschede). These maps are generated based on assumptions that are defined in chapter 2. These maps illustrate same data, implemented on same study area and cope with same user tasks. The usability of each map will be evaluated in the next chapter. 39

51 4. Usability test and results 4.1. Introduction After design phase, in this chapter the usability of designed maps will be evaluated based on three usability characteristics: effectiveness, efficiency and satisfaction. Moreover, the test procedure will be explained and the results will be analyzed to demonstrate which method is the most suitable method for representing transportation network data between three designed maps in chapter 3. In this chapter first the usability and usability testing methods (4.2.), designing usability test (4.3.) and preparing the test (4.4.) will be explained. Also, the usability test results will be evaluated (4.5.) and important problems of maps will be mentioned (4.6) Usability: What is the usability? There are many definitions about the usability and all of them put emphasize on the interaction between a system and the user, e.g. Usability means that the people who use the product can do so quickly and easily to accomplish their own tasks. (Dumas & Redish, 1999, p. 4) Usability relates to whether users can use the system and achieve their goals in a specified context of use with effectiveness (accuracy and completeness), efficiency (minimal resource expenditure) and satisfaction (positive attitudes) (Jokela, et al., 2003). Usability is not the same as quality assurance, zero defects or utility of design features because these terms are more about the product and its utility not the interaction of product with user (Barnum, 2002, p. 6) What is usability testing? Dumas and Redish (1999, pp ) defined five characteristics for every usability test: 1. The usability test helps designer to achieve their goals and primary goal is to improve the usability of a product. The primary goal of a usability test is to improve the usability of the product. The other goal is to improve the process of design and development of a product to avoid the same problems occurring again 2. The participants represent real users The participants should be selected from the group of people who will use the product further. If the participants are more experienced than real users, some problems will remain hidden 40

52 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data and if the participants are less experienced than real users, their comments would not be helpful for a product s usability. 3. The participants do real tasks The participants should do real tasks with a product such as they do on their jobs. By doing real tasks, the results of usability test are more realistic. 4. Observe and record what participants do and say In a usability test, the participants do tasks and make comments about product. All these activities will be observed and recorded to be used for analysing further. 5. Analyse the data, diagnose the real problems, and recommend changes to fix those problems. By analysing the data, the researchers diagnose the product s usability problems and recommend solutions for those problems Goals of usability testing Before selecting any usability test method, the goals should be defined. The analyst should know what information is important and which data should be collected from participants. Even with a sample product, so much happens so quickly in a usability test that if you have not thought about what to focus on, you may miss important events. For each usability test, therefore, you have to start by considering what you want to learn -that is, by defining specific goals and concerns. Defining goals and concerns makes the rest of the planning much easier. (Dumas & Redish, 1999, p. 110) This research aims to evaluate the usability of three designed maps for showing congested parts of the road network in Enschede. To achieve this, this research considers measuring the usability of each map in two groups: generally and specifically. The general and specific goals of usability testing are defined as shown in Table

53 Which method is the most satisfying for users? The general goal of the usability test Which method is most effective? (gives most correct and complete answers to tasks) Which method is most efficient? (users can cope with the tasks in the least amount of time) What are the weaknesses of each map? The correctness of spatial temporal tasks based on spatial Intermediate Elementary and temporal reading levels (effectiveness of each map) Intermediate Intermediate Overall Overall Intermediate Overall Elementary Intermediate Overall Overall The specific goals of this research The time for doing tasks based on spatial and temporal reading levels (efficiency of each map) spatial Intermediate Intermediate Intermediate Overall Overall temporal Elementary Intermediate Overall Elementary Intermediate Overall Overall Understanding participants feeling Table 14: General and specific goals of usability testing Usability testing methods For understanding users reactions to the cartographic visualisation tools, it is not enough to test just the effectiveness of designed maps. Still some answers would be needed about how users deal with designed maps and what are they thinking about. (van Elzakker, 1999). Map designers need this information to improve the usability of maps. By broadening of scope in use and user research in cartography, the qualitative techniques become more applicable and important (Suchan & Brewer, 2000). Van Elzakker and Wealands (2007) mentioned some qualitative methods such as grounded theory, output product analysis, interviews, questionnaires and observation. Dumas and Redish (1999, pp ) mentioned Think aloud method as usability testing method to understand what participants think during the test. In the think aloud method, participants should talk about everything they are thinking about during the usability test. 42

54 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data In the think aloud method, the participants can say their thoughts about a product for each tasks during task execution and they do not have to memorise their comments to say them later. Also, in think aloud method it is no problem for participants to talk during the process and it helps users to concentrate on the tasks. Participants can make comments about their reactions such as confusion or frustration during the test or for just part of the test. Think aloud method leads to valid and the most complete data on cognitive processes (van Elzakker, 1999). But, Think aloud method has some disadvantages too. It is time consuming not just for testing, also in analysing the collected data. To make a clear description of think aloud results, unnecessary variety in the results should be avoided as much as possible. Moreover, the Think aloud method may differ with participants learning styles and some participants do not want to talk during the tasks. In addition, sometimes the participants may not be able to translate their thoughts to words and it can be difficult for them. So, they may be forced to say something what is not exactly what they mean (van Elzakker, 1999) Selecting the usability methods It can be inferred that for measuring the effectiveness, efficiency and satisfaction of user interaction with product, just one method should not be sufficient. To achieve appropriate usability testing, according to the methods characteristics, advantages and disadvantages and the test goals, a combination of some methods would be suitable for measuring the usability of the designed maps. To achieve valid and complete data about cognitive processes, the Think aloud method is applicable. In the Think aloud method, users think aloud while they are doing their tasks and the analyst can use this to recognize their feeling and their think processes. This lets the analyst measure the effectiveness, efficiency and satisfaction of the system to some extent. To measure participants reactions critically, the observation method would be adequate as an additional method. By using the observation method, the analyst can observe participants reactions during the test such as confusion, frustration or gratification. Also by observation method the participant s activities during the test will be observed and recorded and that would be useful for measuring the effectiveness of the system (van Elzakker & Wealands, 2007). In fact, observation method with recordings is an appropriate solution when some information such as participants feeling cannot be perceived well just by questioning (Kumar, 1999, p. 105) To facilitate analyzing the collected data from the Think aloud method, the tasks should be organized somehow to be manageable and well-organized for the analyst. This property helps the analyst to achieve desirable information from the usability test about effectiveness, efficiency and satisfaction. For organizing the tasks and make a structure for the usability test, a questionnaire may be appropriate as a supplement. Questionnaires are structured and facilitate comparability of data by asking participants the same questions, in same order and they do same tasks (Kumar, 1999, p. 109). It isn t enough just to put the question in writing. You also need to put the question into the most specific and appropriate form. The answers to an open-ended question, such as was this product easy 43

55 or difficult to use? won t be useful as the more specific information you d get if you format the question as a structured rating. (Dumas & Redish, 1999, p. 208) To test the usability of three congestion map types of Enschede, the combination of Think aloud, questionnaire and observation methods would be sufficient as usability testing methods. Their synergy covers the weaknesses of each method and the achieved data would be manageable for analysing Deciding who the user should be It has been mentioned before that test participants should be people who will use the products further. The traffic maps of Enschede are designed to show the congested areas and traffic times in Enschede for planners/ traffic managers who deal with transportation network to help them in finding a solution. So, the participants should be from the group of people who deal with transportation networks. Due to the small number of transportation managers of Enschede and the maps had to be evaluated for relatively simple task this research considers potentially future users: PhD students in urban planning and management of Twente University, ITC faculty. This research considers to test the usability of three different maps, so it should be specified how many participants would be needed to test each map. Each participant should test just one map type to avoid occurring learning effects on participants. Nielsen and Molich (1990) found that close to half of the major usability problems would be recognized by three participants. Virzi (1992) found that 80% of the usability problems were detected by 4 or 5 participants and with 10 participants this statistic increases to 90%. Dumas and Redish (1999, p. 127) mentioned that for deciding about the number of participants of usability test some other factors should be considered too such as : 1. How many subgroups would be needed to satisfy usability test goals 2. How much time should be assigned to the test 3. How important the results are. Most usability test includes 6 to 12 participants in two or three groups. Nielsen and Molich s and Virzi s results illustrate that 3 to 5 participants in each subgroup should be appropriate that you are seeing the problems (Dumas & Redish, 1999, p. 128). Most major problems will be uncovered in a usability test with relatively few participants (Virzi, 1992). In this research, 21 users have participated in three groups (each group contained 7 participants) and in each group one map was tested. To invite participants to the usability test, a time schedule is designed and coded to inform users about the test times and help them to manage their times with the schedule. This schedule with a brief description about the test was sent via for users. In these s users are kindly requested to participate in usability test and help the project. 44

56 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data 4.3. Design of the usability test The usability test should be designed in such a way that the analyst can achieve the general and specific goals which have been defined before. So collected data should be directly related to the usability test goals (Dumas & Redish, 1999, p. 189) Questionnaire: In this research the questionnaire is designed based on map tasks, and used to structure the test. Each questionnaire contains 4 parts: 1. The title of test and examiner 2. General questions about the participants 3. Brief introduction to the test and map and participants rights. 4. Tasks which include 12 questions (specific goals) and satisfaction rate (general goals) of the usability test. For each task, 2 questions are considered to prove that participants do not answer the question coincidental or carelessly (Appendix 1and 2) In many usability tests participants do not think aloud well. Some of them forget to think aloud in the middle of the test or some others prefer not to talk when they are thinking (Dumas & Redish, 1999, p. 278). To cover this problem, the tasks in the questionnaire are designed somehow that participants are forced to talk and do the tasks on screen. For answering the questions about tasks in the questionnaire, participants should talk aloud and do the tasks by moving the mouse icon on the screen Observing and think aloud To see what participants do on the screen with the maps, a software is needed to record all activities on the screen. In this research the Snag it software is used to record participants activities on the screen and their voice in think aloud method. This ability helps the analyst to observe the participants activities and listen to their voices to achieve desirable information about tasks. The other tool for observation is the internal camera which is in the front of participant s faces and records their face reactions such as confusion, frustration or satisfaction. In this research a Dell Studio 15 (1558) laptop is used with 2.0 MB camera inside that has adequate resolution for recording face reaction of participants. Moreover, a video camera (Sony camera DCR-SR100/E) is used to record the whole process as a backup Test plan To test each map, first a brief description will be given to explain the procedure for each participant. Then, the participants will answer the general questions and read the map s introduction. Afterwards, they will answer to 12 question on the screen by using the mouse icon, and their reactions on the screen will be recorded by Snag it software and they should talk aloud while they are doing tasks. Their voice will be recorded by Snag it software too and their face reactions will be recorded by the laptop s video camera. The whole process will be recorded by external video camera as a back up to cover the unpredictable problems. 45

57 After the task has been ended, the data about correctness, time, and user s feeling about the tasks would be available for analysis and for measuring the usability of each map Preparing the test Before starting the usability test the environment and test material should be ready Laboratory An appropriate test place would be necessary for each usability test. A suitable environment will reduce external distractions for participants. Also, the furniture and equipments should be placed in suitable position. The environment should be a calm place and furniture should be comfortable for participants Check list (test structure) To achieve a reliable test, the situation should be perfect and similar for each participant. Users participate just one time and if an analyst makes a mistake, he/she may lose the opportunity. Everything should be predicted before users arrive. The check list (test structure) contains 4 parts: 1. Before the user enters 2. Participant arrival 3. Starting the test 4. After the test In this part all important activities which are required for the test are placed. For testing each participant, all of these factors have to be checked. Via a check list, analysts can prepare a controlled and similar situation for every participant. Table 15 illustrates the check list which is used in this research as usability test structure Pilot test The pilot test is an important phase of preparing a test, because it is the last opportunity for recognizing test weaknesses and usability testing problems. Due to this, a pilot test should be considered as a real usability test so the situation such as environment and materials have to be the same as the real test situation to reveal the remained problems. During the pilot test, all problems and defects should be noted and all of them should be modified before testing participants. So, every activity should be considered critically because a negligible problem could make a crisis during the test. In this research all of the usability test activities were checked in pilot test and problems were modified before testing phase to reduce the test defects and increase the usability test quality. Figure 24 shows the usability test environment. 46

58 Analyzing and evaluating the usability of linear visual representations and diagram maps for representing transport network data Before the user enters 1 Setup camera ( check camera ) 2 Setup position (check the chair of participant position and lap top position) 3 Prepare the questionnaire for the participant 4 Take care that there is a pen for participant s answering 5 Prepare the snag it software and turn the webcam on to be ready for recording 6 Prepare the map on screen 7 Check the light of the room Participant arrival 1 Hello and welcome to our test, we are very pleased to see you here. Please take a seat on the chair in front of the laptop 2 This is your questionnaire, please read this carefully 3 First, there are general questions about yourself and then an introduction about the test, and then you will see 12 tasks and you are kindly requested to answer them using the think aloud method. 4 (brief introduction about think aloud method and map) 5 Your name and results will be kept private and the test results are just for the evaluation of this map s usability. 6 Please first answer the general questions. 7 And then please read the introduction carefully. After you finish reading the map introduction, the test will be started. 8 Do you have any question? (answer if there is a question) Shall we start? Starting the test 1 Run the snag it and say : your activities on the screen will be recorded now 2 Run the webcam and say: your reactions will be recorded now 3 Start recording by camera 4 Please start and please do not forget to think aloud 5 After finishing the tasks please write your suggestions for improvement of the map and tell me to stop the process when you are ready. 6 Thank you for your cooperation After test 1 Save the video file of the Snag it 2 Save the webcam file 3 Camera off 4 Thank participant for giving his/her time check Table 15: the check list which is used in this research as usability test structure 47

59 Figure 24: the test environment 4.5. Usability test analys and results In this chapter the usability test results will be evaluated generally and specifically. In the general evaluation, the effectiveness, efficiency and satisfaction of each three designed maps (flow map, isopleth map and diagram map) will be measured based on their total average of correctness, task completion time and participants face reactions. In the specific evaluation, the effectiveness, efficiency and satisfaction of each three designed maps will be measured based on the combination of spatial and temporal reading levels. But, at the first, for analysing the achieved data from the test, some quantitative criteria for each measure should be defined to organize test results Criteria For analysing test results, some criteria are defined to facilitate the comparison of usability between the three designed maps and also, to achieve quantitative results from the test. The following criteria help the analyst to measure the differences between Flow map, Isopleth map and Diagram map. 1. Correctness: to measure the correctness of each map, the answers are divided into two groups: acceptable and not acceptable. means that users understands the nature of the map and do the tasks correctly. acceptable means that a user does not understand the map and does not answer correctly. Moreover, random answers or careless answers are considered as not acceptable. 2. Satisfaction: to measure the satisfaction of each map, the participants face reactions are divided to two groups: satisfied and not satisfied. Satisfied means that the participants answer the questions confidently. satisfied means participants are seen confused, frustrated or not confident about tasks Data organization To arrange collected data from participants, some tables are designed to encompass all data about each participant such as correctness, face reactions (feeling), time and their comments of each tasks (Appendix 3). This table (Figure 25) facilitates gathering and analysing usability test results for both general goals and specific goals. 48