A Conceptual Model for Analyzing Contribution Patterns in the Context of VGI

Transcription

1 A Conceptual Model for Analyzing Contribution Patterns in the Context of VGI Karl Rehrl, Simon Gröechenig, Hartwig Hochmair, Sven Leitinger, Renate Steinmann and Andreas Wagner Abstract The chapter proposes a conceptual model as foundation for analyzing user contributions in the context of VGI. The conceptual model is based on a set of action and domain concepts, which are combined to a task-model describing typical tasks of volunteered geographic information contribution. As a proof-of-concept, the model is applied to two sample data sets that are extracted from the OpenStreetMap (OSM) change history. OSM data samples provide a proof-of-concept concerning the applicability of the model for crowd activity analysis. The resulting contribution graph, which is a graph-like structure of linked editing actions, can be used as foundation for analyzing complex contribution patterns. Keywords VGI Crowd activity Contribution analysis Editing patterns Conceptual model K. Rehrl (&) S. Leitinger R. Steinmann A. Wagner Salzburg Research, Jakob Haringer-Straße Salzburg, Austria karl.rehrl@salzburgresearch.at S. Leitinger sven.leitinger@salzburgresearch.at R. Steinmann renate.steinmann@salzburgresearch.at A. Wagner andreas.wagner@salzburgresearch.at S. Gröechenig Carinthia University of Applied Science, Europastraße Villach, Austria simon.groechenig@edu.fh-kaernten.ac.at H. Hochmair Fort Lauderdale Research and Education Center, University of Florida, 3205 College Avenue, Fort Lauderdale, FL , USA hhhochmair@ufl.edu J. M. Krisp (ed.), Progress in Location-Based Services, Lecture Notes in Geoinformation and Cartography, DOI: / _21, Ó Springer-Verlag Berlin Heidelberg

2 374 K. Rehrl et al. 1 Introduction The term Volunteered Geographic Information (VGI) denotes geographic information, which is collectively contributed by a heterogeneous crowd of voluntary people. Over the last years, VGI has gained increasing interest in the GI research community (Goodchild 2007). VGI is considered as a serious source for geographic information (Goodchild 2007; Kuhn 2007), even more triggering a change in information production while challenging science as well as businesses (Budhathoki et al. 2010). While most of the research methods from GI science could be applied to VGI as well (Kuhn 2007), new research strands such as VGI digital spatial data exchange, collaborative planning through VGI, or societal impacts of VGI (Elwood 2008) are opened. Budhathoki et al. (2010) propose a three-tiered conceptual framework for VGI, which provides a good reference frame for classifying VGI-related research. The framework is composed of the three arenas Motivation, Action and Interaction and Outcome. Most of the VGI-related research so far can be classified in one of the three arenas. Recent work addresses questions about the motivation of VGI contributors (Budhathoki et al. 2010; Coleman and Georgiadou 2009; Coleman 2010), different interaction patterns (Mooney and Corcoran 2012a) and the quality of the outcome (Neis et al. 2011). In addition to the three arenas, Budhathoki et al. detail the arenas with subarenas. For example, in the context of the arena Action and Interaction the conceptual framework defines the three sub-arenas Structure, Action, Norms/Rules-in-use. The sub-arena Norms/Rules-in-use addresses rules within the community, e.g. what contributors of VGI projects should do or not do. Structure is the result of applying rules. Action addresses questions of how people actually contribute within the constraints of structure. While the proposed arenas and sub-arenas provide a good overall frame, more detailed conceptual models for analyzing one of the sub-arenas are still missing. This work proposes such a conceptual frame for the sub-arena Action, which subsumes all kinds of user interaction with the emphasis on information contribution. The remainder of the chapter is structured as follows: The next section introduces related work on editing actions in the context of VGI. The following section proposes a set of action and domain concepts as foundation of editing patterns. In the subsequent section action and domain concepts are combined to editing actions representing typical editing patterns. The section afterwards shows a proof-of-concept with sample data from the OpenStreetMap project, which is followed by conclusions and an outlook on future work. 2 Related Work Currently there are two different research strands to analyze action and interaction in the context of VGI: One is a user-centric strand and the other is a data-centric strand. User-centric means that the analysis starts from the motivation of

3 A Conceptual Model for Analyzing Contribution Patterns 375 individual users (Budhathoki s Motivation arena) and their activities (Budhathoki s Action & Interaction arena) and generalizes contribution behavior over specific user groups. Typical research questions are How do users contribute?, Which roles can be attributed to users or user groups? or Is it possible to identify different interaction styles based on individual user contributions?. The other strand is a data-centric one, putting the collective outcome and not the individual user in focus ( Outcome arena). Typical research questions are Which features are in the dataset? or Which updates happened to a feature? or Which features are missing?. The main goal of this research strand is to identify feature-related activity patterns. One of the newer approaches to investigate action and interaction in the context of VGI is to analyze editing histories of datasets. Some of the VGI projects store a complete history of all dataset updates, e.g. the most prominent VGI project OpenStreetMap (Haklay and Weber 2008), which could be used to analyze editing behavior of the crowd. But even without a complete change history crowd activity may be reconstructed with regular database snapshots. Over the last years, some authors have started to analyze crowd activity of VGI projects, specifically using the OpenStreetMap history dump. Recently, Mooney and Corcoran followed the user-centric strand with investigations on social interactions in the OSM London dataset (Mooney and Corcoran 2012a). Their research addressed the question whether editing profiles could be extracted from the contribution history. Haklay et al. (2009) tackled the question of how many users it takes to map an area well. Mooney and Corcoran (2012b) also followed the data-centric strand. The authors analyzed the distribution of users contributing to edits in heavily edited features in OpenStreetMap. The authors also proposed an algorithm to access the Open- StreetMap history dump (Mooney and Corcoran 2011). van Exel et al. (2010) state that both strands are intertwined since data-centric editing patterns are closely related to user-centric ones (because any editing action is bound to a user). Nevertheless, the question of action in VGI projects is tackled from different perspectives and thus a conceptual model could help to integrate both strands. 3 Towards a Conceptual Model for Editing Actions in the Context of VGI One of the first questions related to a conceptual model of user actions is: What are typical user activities in the context of VGI?. Related work distinguishes at least four different action and interaction activities (Budhathoki et al. 2010; Ramm and Topf 2010): (1) contributing geographic information (e.g. creating and editing features), (2) building community structures (e.g. organizing mapping parties, operating mailing lists), (3) working on norms and rules (e.g. contributing to definitions in the OSM Wiki) and (4) working on community tools (e.g.

4 376 K. Rehrl et al. contributing to editors like JOSM). The last activity is not explicitly mentioned in related work, but is a necessity of VGI projects, too. Each of the identified user activities can be further detailed into concrete action and interaction patterns. For example, the user activity contributing geographic information can be further detailed in the following sub-activities: (1) collecting information (e.g. GPS traces, street names, speed limits), (2) editing features (e.g. drawing features, adding attributes, changing attributes and attribute values, deleting features) and (3) submitting edits to the database. Sub-activities are considered a good starting point for a conceptualization process. While sub-activities could be identified for any of the aforementioned activities, in this work we focus only on the activity contributing geographic information. We assume that any activity related to geographic information contribution directly affects the dataset and thus can be derived from the change history. According to Guarino (1998), a conceptualization is the formal structure of reality as perceived and organized by an agent, independently of the vocabulary used or the actual occurrence of a specific situation. In order to conceptualize user actions in the context of volunteered geographic information contribution, we have to conceptualize actions ( How do users contribute? ) and geographic information ( What is the result of actions? ). 3.1 Action Concepts One of the approaches for conceptualizing user actions (task modeling) is to build on the conceptual frameworks of activity theory (Kuuttii 1996). The principle of activity theory is to define a minimal meaningful context for individual actions. Activity theory structures user activities with the following hierarchical layers: Activity: A sequence of actions following a certain motive. Typically an activity follows a certain strategy. Action: A sequence of operations for reaching a certain goal. Actions have a cognitive component. Operation: The most granular level. Operations are atomic and represent welldefined habitual routines. As Kuhn (2001), states activity and action layers may contain several hierarchical sub-structures. Timpf (2001) proposes four different approaches for deriving geographic task-models: (1) task analysis, (2) information on past task-analyses, (3) analysis of GIS products and (4) applying knowledge from knowledge engineering. In our conceptualization we combine different approaches. We build on information from previous task-analyses (e.g. information from related work), we analyze typical tasks of VGI contributors (e.g. by means of self-experiments as well as community workshops) and we analyze tools, especially those available as open source in the context of OpenStreetMap. Building on these information sources we define the following VGI specific layers for structuring user activity:

5 A Conceptual Model for Analyzing Contribution Patterns 377 VGI Activity: A sequence of consecutive actions (information contribution) by a single volunteering user or a group of volunteering users. Activities could be structured in different dimensions: (1) by users (all actions by one user or a group of users), (2) by location (all actions in a certain geographic region), (3) by action type (all actions belonging to the same or a similar type, e.g. create, edit, delete), (4) by information category (all actions contributing to the same information category, e.g. streets, land use, buildings) and (5) by time. VGI Action: A sequence of consecutive operations by a single volunteering user within a timespan. A typical user action is a certain manipulation of a single geographic feature. VGI Operation: An atomic operation on a single geographic feature, e.g. creating the geometry, modifying the geometry or adding an attribute A Basic Set of VGI Operations If we assume that geographic information is stored in a database, the four basic operations for persistent data storage (CREATE, READ, UPDATE, DELETE, also called CRUD) are at the heart of any conceptual model (James 1983). Following these basic operations, any contribution to a VGI dataset by a volunteered user may be drilled down to one of the aforementioned operations: CREATE, UPDATE and DELETE (READ could also be considered as a concept, however, since it makes no changes to the dataset, it is not relevant for contributions). It is worth to mention that each operation has to be uniquely attached to a single user and a timestamp. The resulting conceptual model for VGI operations and their relationships to action and activity concepts is shown in Fig. 1. We further assume that the aforementioned database operations may be executed on different information items, depending on the geographic information domain. For example, if the operation CREATE is executed on a geographic feature, it could be detailed to the operation CREATE FEATURE. In order to further detail operations, a conceptual model for the geographic information domain has to be defined. We call the concepts representing information items domain concepts. The conceptual model for action and activity layers is proposed in a later section, by combining action and domain concepts. 3.2 Domain Concepts Domain concepts are considered as conceptualizations of real-world phenomena in the geographic domain (Mark et al. 2001). In related work serveral conceptualizations of geographic phenomena have been proposed (Goodchild 2010). Most of the current GIS are based on object-based conceptualizations of real-world phenomena (Câmara et al. 2009). One such commonly used model is the OpenGIS Abstract Specification, Topic 5: Features (Kottman and Reed 2009) specified by

6 378 K. Rehrl et al. Fig. 1 Relationships between operation, action and activity concepts the Open Geospatial Consortium (OGC). Instead of developing a new conceptual model, our approach builds on the OGC specification and adapts this specification to the requirements of VGI. The OGC specification introduces the concept of a geographic feature as representation of a geographic phenomenon. Each feature is composed of a geometry, which is bound to a spatial reference system and a feature type. A feature type defines a set of attributes which is used to describe the feature. Features have a flat structure (e.g. other features may not be part of a feature). In addition to the feature specification the OpenGIS Abstract Specification, Topic 8: Relationships between Features (Kottman 1999) adds the notion of relationships. Relationships are necessary to structure feature groups and feature hierarchies. Since the OpenGIS Abstract Specification is a generic approach for modeling geographic phenomena it is considered a good conceptual foundation for modeling VGI, too. However, VGI projects typically do not build on OGC specifications due to various reasons (e.g. complexity, missing freedom) and come with their own, community-driven models. Despite of a number of differences, we also found similarities such as the notion of a map feature as digital representation of geographic phenomena in OpenStreetMap. 1 However, the description of features does not follow strict rules like feature types in the OGC model, but is communitydefined. In many VGI projects the minimal necessity for the definition of a geographic feature is a geometry (at least a pair of coordinates). Meaning is attached to geometries with a set of optional key-value pairs (so-called tags). In order to build a VGI database like OpenStreetMap any community has to agree on a set of rules for sucessful collaboration (e.g. OpenStreetMap relies on a minimal data model and a community-driven Wiki describing domain concepts). The definition of useful attribute sets is an ongoing community process documented in the OSM Wiki. There are always several proposals how to tag features and it typically takes some time until the community agrees on one of the proposals (e.g. see Proposed Features in the OSM Wiki). In OpenStreetMap exists a well-established concept called primary feature, which comes near to the notion of a feature type, but it is not strongly typed. Since there is no strict validation in the data submission process, it is possible to submit a feature geometry to the OpenStreetMap database while omitting tags. 1

7 A Conceptual Model for Analyzing Contribution Patterns 379 Having these differences in mind, our approach for a conceptual domain model builds on some of the concepts of existing models, but adds adaptations according to the needs of VGI. At least the model has to be capable of missing feature types as well as feature types with differing attribute sets (tag sets). We assume that attributes or attribute values do not follow strict rules and any attribute as well as any attribute value may be committed to the database. Although these findings are mainly based on VGI in the context of OpenStreetMap, we consider Open- StreetMap as being prototypical for similar VGI projects. It is worth to mention that the model is based on an object-based conceptualization of geographic phenomena and we assume that the spatial reference is described as vector in a 2-dimensional geometrical space. The model does not fully cope with other notions of VGI such as geo-tagged multimedia content (e.g. geo-tagged photographs at Flicker or geo-tagged Twitter messages). We further assume that the need for a relaxed conceptual domain model can be attributed to the aspect volunteered in VGI, providing the community with a high degree of flexibility and freedom. Ramm and Topf state The intention of the OpenStreetMap project always was to implement the simplest thing that could possibly work. (Ramm and Topf 2010). This statement could be possibly taken as synonym for the flexibility and freedom of VGI projects. In order to avoid any confusion between our conceptual domain model for VGI and the OpenGIS Abstract Specification, we call our domain model Volunteered Feature Specification (VFS). At the heart of the specification is the notion of a Volunteered Feature (VF), which is conceptually similar to the OpenGIS Feature Specification, but adds the following relaxations for being compatible to VGI dataset instances: A Volunteered Feature (VF) is bound to a Volunteered Geometry (VG), but may exist without a Volunteered Feature Type (VFT) and thus a VF is considered not strongly typed. The specification of a Volunteered Geometry (VG) is based on the geometry types in the OGC OpenGIS Object Model, but adds simplifications (Fig. 2). A Volunteered Feature Type (VFT) is composed of a primary volunteered attribute, which defines the VFT. Volunteered Attributes (VATT) may be freely attached to VFs without following a strict scheme. The definition of VATTs and their values does not follow a strict scheme, but allows for arbitrary values. Schemes for VFTs and rules for attaching VATTs to VFs are community-defined. A typical medium for specifying the rules is a community Wiki. A Volunteered Relation (VR) defines relationships between arbitrary VFs. As proposed in the OpenGIS Abstract Specification, Topic 8, Relationships between Features, VFs may have different VGs (e.g. points and polygons) and VFTs (e.g. features composing a public transport station). VRs may be recursive, meaning that VRs may include other VRs. Figure 2 illustrates the proposed model of domain concepts as UML class diagram.

8 380 K. Rehrl et al. Fig. 2 Class diagram for modeling volunteered features 4 Combining Action and Domain Concepts By now we have defined the conceptual basis for modeling actions (task-centric view) and the domain of geographic information (domain-centric view). A combination of both would facilitate a conceptual model being capable of dealing with arbitrary editing actions. The first step towards a combined conceptual model is to define, which operation may be executed on which type of volunteered feature. As foundation for action concepts we defined a set of three atomic operations: CREATE, UPDATE, DELETE. In combination with the domain concepts Volunteered Feature (VF) and Volunteered Relation (VR) the following combined operations could be derived: CREATE VF, UPDATE VF, DELETE VF, CREATE VR, UPDATE VR and DELETE VR. From the domain model we assume that a VF is always created with a VG (volunteered geometry). If the VF gets deleted, also the VG is deleted. From the domain model we further derive that if a VF exists, it may be updated in the following ways: ADD VFT, ADD VATT, REMOVE VFT, REMOVE VATT, MODIFY VG, MODIFY VATT and MODIFY VFT. Thus, the action model has to be extended with the following operations ADD, REMOVE and MODIFY, which further detail the operation UPDATE. Table 1 lists possible combinations of operations and VFs/VRs. The resulting set of operations already considers the previously defined relaxation rules for VFs. For example, the scheme allows to CREATE a VF without Table 1 Conceptual scheme for combining action and domain concepts Operation Volunteered feature (VF) Volunteered relation (VR) CREATE VF (VG) VR DELETE VF (VG) VR ADD ATT, VFT VFT, VATT, VF, VR REMOVE ATT, VFT VFT, VATT, VF, VR MODIFY ATT, VG VFT, VATT

9 A Conceptual Model for Analyzing Contribution Patterns 381 specifying the VFT or it is possible to ADD arbitrary VATTs without relying on a strict scheme of feature types. For simplicity we call combinations of operation and domain concepts domain operations. In addition to the overall scheme for domain operations, Table 2 further details the conceptual scheme with possible relationships between operations and OpenGIS Simple Geometry Types. 4.1 Towards Actions: Rule-Based Aggregations of Domain Operations Based on action and domain concepts, the model can now be extended to the action and the activity layers. In contrast to operations, actions have to fulfill the following requirements: (1) the action can be fully described with a sequence of one or more domain operations, (2) each operation has to be executed by the same single user, (3) each operation has to be executed at a single moment in time and the timestamps of sequent operations have to be consecutive, meaning that no other operation of the same user has been executed in between and (4) the action fulfills a goal-oriented manipulation of a VF or VR. As an example we describe an instance of the action concept contribution of a feature, which can be defined as a sequence of the following domain operations: (1) CREATE VF, (2) ADD VFT (optional), (3) ADD VATT (optional) and (4) ADD VATT (optional). If necessary, the action could be further detailed with more specific actions like create point feature or create line feature. It is important to mention that the concept of an action is inherently seen as a rule-based aggregation over domain operations. Thus, by adding aggregation rules for domain operations, as many actions as necessary could be defined. In order to demonstrate the applicability of the approach, we define a set of possible actions for VGI contributions (Table 3). The proposed action set is derived from typical user-tasks in the context of Open- StreetMap, but could be most likely applied to other VGI projects as well. 4.2 Towards Activities: Rule-Based Filtering of Action Sets According to activity theory, user activities are based on concrete motives. In the context of VGI typical motives are: users strive towards fully mapping their local Table 2 Operations in relationship to OpenGIS simple geometry types Operation Point Line Linear ring Polygon CREATE X X X X DELETE X X X X ADD Point Point Linear ring REMOVE Point Point Point MODIFY VG, VATT VATT, VG VATT, VG VATT, VG

10 382 K. Rehrl et al. Table 3 Proposed action set for describing VGI contribution tasks Action Description Create point VF A point feature with a point geometry is created Update point VF The spatial reference of a point VF is modified Delete point VF A point VF is deleted Create line/polygon VF A VF with a line or polygon geometry is created and a VFT is added Update line/polygon VF The spatial references of a line or polygon geometry are modified Delete line/polygon VF A VF with a line or polygon geometry is deleted Add points line/polygon VF One or more additional point VFs are added to a line or polygon VF Remove points line/polygon VF One or more point VFs are removed from a line or polygon VF Split line/polygon VF A line or polygon VF is split into two VFs Merge line/polygon VF Two line or polygon VFs are merged to one VF Create VR A relation is created Delete VR A relation is deleted Add member VR One or more VFs are added as members to a VR Update member VR The role of one or more members is modified Remove member VR One or more VFs are removed from a VR Add VFT VF/VR A primary attribute is added to a VF or VR Update VFT VF/VR The primary attribute of a VF or VR is modified Remove VFT VF/VR The primary attribute of a VF or VR is removed Add attributes VF/VR One or more attributes are added to a VF or VR Update attributes VF/VR An attribute value of one or more attributes is modified Remove attributes VF/VR One or more attributes are removed from a VF or VR surrounds, users strive at getting the number one in the (local) community or users strive towards a high level of positional accuracy of their contributions. Thus, it makes sense to define an activity as a group of actions following specific motives. Thus, in order to group actions to activities, actions have to be filtered by one or more criteria derived from one or more motives. Table 4 proposes possible filter rules for action sets. 5 Proof-of-Concept: Applying the Model on a Real-World Dataset In order to prove the concept we apply the model on the OpenStreetMap change history. OpenStreetMap is one of the most relevant VGI projects and thus considered a good example for a proof-of-concept. On the one hand, due to the open license, the OSM dataset is of high value for the research community. On the other hand, the OSM community explicitly specifies the structure for interactions with

11 A Conceptual Model for Analyzing Contribution Patterns 383 Table 4 Proposed activity groups and filter rules for action sets Activity criteria Filter rules for action sets By users All actions of a single user or a specific user group, e.g. female users By location All actions in a certain region, e.g. in UK By action type All actions of a certain type, e.g. creations of point features By information category All actions manipulating features of a certain feature type, e.g. land use, streets, buildings By time All actions within a certain timespan, e.g. during a month Mixed criteria Filter rules with different criteria, e.g. all creation actions of point features of female users in London the OSM database in the OSM Wiki. 2 For deriving action and operations concepts we analyzed the OSM Wiki, especially the part on the OSM API, 3 related literature (Ramm and Topf 2010) as well as editing tools such as JOSM. 4 Operation concepts in OpenStreetMap are widely based on the CRUD paradigm. Domain concepts are specified in the OSM Wiki. The conceptual data model is rather simple and based on the concept of VFs. In OSM a VF could be a node or a way, depending on the VG. Linear Rings are modeled as a specific form of ways with the same start and end node. Polygons are either modeled as Linear Ring or as relation. The concept of VATT is called tag and the concept of a VFT is represented by the notion of a primary tag. In addition to VFs, the OSM data model also introduces the concept of relations, which is defined in analogy to the aforementioned VR concept. Table 3 instances the previously defined Volunteered Feature Specification (VFS) with the OpenStreetMap data model. 5.1 Building Model Instances from the OSM Change History We test the conceptual model with sample data from the OSM change history. The OSM history includes all changes back to October 2007 (although the project was started in 2004, due to a change in the API the history is only accessible back to 2007). The basic algorithm for accessing the data has been previously described (Mooney and Corcoran 2011). For extracting the data using the OSM API we developed a standardized process (Fig. 3). This process is capable of building a graph-like representation of domain operations and action aggregates for arbitrary features or feature sets (within a configurable bounding box). We conducted a preliminary test of the model with OSM data for different geographic regions in Europe and the US. In order to get first results concerning crowd activity we applied the extraction process on sample data from two Austrian

12 384 K. Rehrl et al. Fig. 3 UML activity diagram showing the data extraction and model building process for OSM cities (Linz and Villach) for the years 2010 and Figure 4 shows two maps of the inner city districts and the bounding boxes (195,488 and 212,891 m 2 ) we used for data extraction.

13 A Conceptual Model for Analyzing Contribution Patterns 385 Fig. 4 Bounding boxes for sample data extraction from the cities of Linz and Villach in Austria Table 5 lists some contribution indicators. All indicators are calculated from the change history data within the bounding boxes. A first comparison of editing activity in both cities shows that OSM mappers in Linz are by far more active compared to mappers in Villach (Fig. 5a). While there was a significant increase in editing actions (per user and year) in Linz from 2010 to 2011, this value remained nearly equal in Villach (although the number of mappers doubled in Villach and reached the number of mappers in Linz). Also the average number of editing actions per feature is lower in Villach, although there has been a significant increase from 2010 to 2011 (Fig. 5b). The mapper/inhabitant ratio (number of mappers per 1,000 inhabitants) reveals that there is an equal or better established OSM community in Villach compared to Linz. We consider the first results as good proof of the conceptual model as well as the extraction process. But we are also aware that the proposed approach can only be the foundation for a punch of analysis in the context of more detailed investigations on crowd activity. Table 5 Contribution indicators for the years 2010 and 2011 extracted from the OSM change history Linz (2010) Linz (2011) Villach (2010) Villach (2011) Active mappers Mappers/inhab. (91000) Number of operations 4,644 8, ,194 Number of actions 1,222 2, Average. op./user/year Average actions/user/year Average op./feature Average actions/feature

14 386 K. Rehrl et al. Fig. 5 Comparison of mapper activity over 2 years in two Austrian cities Table 6 OSM domain operation concepts as instances of the conceptual model Node, way (VF) Relation (VR) Operation Node (point) Way (line) Closed way (linear ring) Relation (polygon, multipoint, multiline, multipolygon) CREATE X X X X DELETE X X X X MODIFY X X X X ADD Tag Tag, node Tag, node Type, member (node, way, closed way, relation), tag REMOVE Tag Tag, node Tag, node Type, member (node, way, closed way, relation), tag UPDATE Coordinates, tag Tag, node, startend Tag, node, startend Type, tag 6 Conclusions and Outlook Analyzing patterns of user contributions in the context of VGI has gained considerable attention over the last years. VGI projects such as OpenStreetMap foster this research strand by offering access to the full history of changes. Although some authors have already analyzed minor parts of the dataset, the question of how to conceptually deal with the data still remains. The paper proposes a conceptual model as a foundation for a uniform and standardized process for analyzing user contributions. Although the paper only proves the concept of the proposed model with one VGI project (OpenStreetMap), we assume that instances of the conceptual model could be adapted to other VGI projects as well. The proposed conceptual model has to be adapted in the following way: (1) define a new instance

15 A Conceptual Model for Analyzing Contribution Patterns 387 of the model (similar to the instance we propose for OSM in Table 6), (2) adapt action concepts and aggregation rules and (3) adapt the process for accessing contribution data (Fig. 3). The proposed approach closes the gap between user contribution data and a conceptual model laying the foundation for comparable analysis of contribution patterns. It is worth mentioning that the proposed approach is only applicable to a VGI project if data about user contributions is accessible. This is the case for some VGI projects (e.g. OpenStreetMap), but not for others (e.g. Google Map Maker). 5 The proposed conceptual model is considered as a first step towards more complex analyzes of crowd activity. At the end of the proposed extraction process we store operations and actions as a graph-like structure which we call contribution graph (e.g. a graph database like Neo4j 6 could be used). We expect a contribution graph to be a universal basis for complex analysis, especially for having a closer look at different kinds of crowd activities. One of the possible future research directions is to find prototypical contribution patterns leading to good or bad data quality. Identifying such patterns is considered a necessary step in the definition of quality indicators for VGI. References Budhathoki NR, Nedovic-Budic Z, Bertram B (2010) An interdisciplinary frame for understanding volunteered geographic information. Geomatica 64(1): Coleman DJ (2010) The potential and early limitations of volunteered geographic information. Geomatica 64(2): Coleman DJ, Georgiadou Y (2009) Volunteered geographic information: the nature and motivation of producers. Int J Spat Data Infrastruct Res (Special issue GSDI-11) Câmara G, Vinhas L, Clodoveu D, Fonseca F, Carneiro T (2009) Geographical information engineering in the 21st century. In: Research trends in geographic information science, Springer, Berlin Elwood S (2008) Volunteered geographic information: key questions, concepts and methods to guide emerging research and practice. GeoJournal 72(3 4): Goodchild MF (2007) Citizens as sensors: the world of volunteered geography. GeoJournal 69(4): Goodchild MF (2010) 20 years of progress: GIScience in J Spat Inf Sci 1:3 20 Guarino N (1998) Formal ontology and information systems. In: Using ontologies for integrated geographic information systems, IOS Press, Amsterdam, pp 3 15 Haklay M, Basiouka S, Antoniou V, Ather A (2009) How many volunteers does it take to map an area well? the validity of Linus law to volunteered geographic information. Geog J 47(4):1 13 Haklay M, Weber P (2008) OpenStreetMap: user-generated street maps. IEEE Pervasive Comput 7(4):12 18 James M (1983) Managing the data-based environment. Prentice Hall, New Jersey Kottman C (1999) The OpenGIS abstract specification, topic 8: relationships between features

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