Chapter 1. GIS Fundamentals

Transcription

1 1. GIS Overview Chapter 1. GIS Fundamentals GIS refers to three integrated parts. Geographic: Of the real world; the spatial realities, the geography. Information: Data and information; their meaning and use. Systems: The computer technology and support infrastructure. GIS therefore refers to a set of three aspects of our modern world, and offers new ways to deal with them (Davis, 21). In 1990, the President of the Association of American Geographers, Saul Cohen, was quoted: Times are changing, and our methods of meeting the needs of the times are also changing. The world is entering the post-industrial Information Age a time when information is becoming a major product of, and foundation for, progress. Increasing emphasis on data management is apparent and necessary. Today s focus in geography (or any other discipline) on data handling and data manipulation reflects the national (and international) emphasis on meeting the needs of the postindustrial information age. The concept of information is indeed the heart of the rapidly growing field of Geographic Information Systems or GIS. As the world moves into the Information Age, meaningful data and information are becoming the major currency. With the continuous advances in computer technology, it is easy to concentrate on dazzling systems and software, but the real value of any product is the data and the information such data provides. At the heart of any GIS is information. This chapter introduces the reader to the very basic principles of Geographic Information Systems, by giving an overview of the different operations that it can handle and perform, as well as its environment. It aims to explain what GIS is, and presents the ArcView Graphical User Interface. 2. What is GIS? 2.1 History of GIS Spatial analysis has been around as long as maps have been used for navigation. Traditional GIS has included paper maps, and manual tools that were utilized before the computer age. There are many theories on how and where the original GIS began and took hold in the information-based world we live in today. There is little doubt that the Harvard Laboratory for Computer Graphics, later renamed by adding and Spatial Analysis to its title, was a key institution in the birth and early development of GIS in the United States. A large number of the founders of GIS in the academic and commercial sectors spent time at the Harvard Lab in the 1960s and 1970s, as staff, students, or visitors, exchanging ideas that would shape the field. Work Site Alliance Community Based GIS Education 1

2 Most would acknowledge that the two dominant commercial GIS producers in the United States are Environmental Systems Research Institute (ESRI) and Intergraph. Estimates usually indicate that together they produce at least half of the GIS software in the country. ESRI will be the focus of this chapter, with the ESRI desktop application ArcView being utilized for the software application of this course. Jack Dangermond, the President of ESRI, Inc. since 1969, is well known to GIS users because he established the company in that year, then subsequently developed and launched ARC/INFO in Dangermond continues to refine ESRI s software, and his efforts qualify him as one of the original thinkers in the development of spatial analysis systems. (Lakhan, 2) 2.2 GIS Description Geographic Information Systems (GIS) are computerized systems for the storage, retrieval, manipulation, analysis, and display of geographically referenced data. Since they can include either physical, biological, cultural, demographic, or economic information, they are valuable tools in natural, social, medical, and engineering sciences as well as in business and planning. The infrastructure to any GIS is made up of four components whose interrelation is shown on the illustration below. These components can be listed in order of importance as follows. Methods and People The most important part of a GIS infrastructure. Although GIS is a powerful tool, it will not work without some well-adapted methods and trained people. Data The needed raw material to be processed by the system. The focus and attention should be on data. In fact, most work will be devoted to data input and management. Data (information) is the foundation of GIS applications. Software The computer programs needed to run GIS. There are many GIS programs available, from low-cost and low-performance packages to expensive and very powerful ones. This also includes support programs, such as statistical, word processing, graphing, and others. Hardware The machinery on which GIS operates computers, printers, plotters, digitizers, and other types of equipment. (Davis, 25) Figure 1.1. Components of a GIS. Work Site Alliance Community Based GIS Education 2

3 Unfortunately, GIS is often developed in the wrong order and more attention is given to the dazzling hardware and software, rather than trying to fit the data to the computer technology. The statement garbage in; garbage out can be applied to the data collection process for the organization and the people who utilize and implement that data. The greatest piece of software, and the computers with the greatest amount of memory and speed, will not improve the information from data that is poorly gathered and inputted into the system. 2.3 General Purposes of GIS A description of GIS is that it is a computerized system that deals with spatial data. GISs essentially perform five processes or tasks. Input Manipulation Management Query and Analysis Visualization Input Gathering data from many sources. Before geographic data can be used in a GIS, the data must be converted into a suitable digital format. Today many types of geographic data already exist in GIS-compatible formats. These data can be obtained from data suppliers and loaded directly into a GIS. (ESRI, Inc.) Manipulation Converting data from one form to another; that is, conversion from one geometric projection to another, re-scaling, and other computer tricks to make the data more useful; changing one map file to match another. It is likely that data types required for a particular GIS project will need to be transformed or manipulated in some way to make them compatible with your system. For example, geographic information is available at different scales (detailed street centerline files; less detailed census boundaries; and postal codes at a regional level). Before this information can be integrated, it must be transformed to the same scale (degree of detail or accuracy). This could be a temporary transformation for display purposes or a permanent one required for analysis. GIS technology offers many tools for manipulating spatial data and for weeding out unnecessary data. (ESRI, Inc.) Management and Storage Efficient digital storage and retrieval for easy, efficient selection and viewing of data in a variety of ways. This involves administering and keeping track of data, including integration of various data sets into a common database. For small GIS projects it may be sufficient to store geographic information as simple files. However, when data volumes become large and the number of data users becomes more than a few, it is often best to use a database management system (DBMS) to help store, organize, and manage data. A DBMS is nothing more than computer software for managing a database. There are many different designs of DBMSs, but in GIS the relational database design has been the most useful. In the relational design, data are stored conceptually as a collection of tables. Common fields in different tables are used to link them together. This surprisingly simple design is so broadly used Work Site Alliance Community Based GIS Education 3

4 primarily because of its flexibility and very wide range of applications both within and outside of GIS. (ESRI, Inc.) Query and Analysis Manipulating data to produce insight and new information. Simplifying the data or the world and its processes to understand how things work. Once you have a functioning GIS containing your geographic information, you can begin to ask simple questions such as: Who owns the land parcel on the corner? How far is it between two places? Where is land zoned for industrial use? And, analytical questions such as: Where are all the sites suitable for building new houses? What is the dominant soil type for oak forest? If I build a new highway here, how will traffic be affected? Visualization Presenting data in various ways for easy understanding of maps and reports (Davis, 23). For many types of geographic operations, the end result is best visualized as a map or graph. Maps are very efficient at storing and communicating geographic information. While cartographers have created maps for millennia, GIS provides new and exciting tools to extend the art and science of cartography. Map displays can be integrated with reports, three-dimensional views, photographic images, and other output such as multimedia. (ESRI, Inc.) 3. AreView Graphical User Interface (GUI) User Interface is a generic term, in computer science, which is adopted for all components that humans use to communicate with computers. It includes anything between the input devices (keyboard, mouse, etc) and the output devices (printer, video display monitor, etc) which translate the electronic signals sent back by the machine to the user. Graphical User Interface (GUI) designs a display format that enables the user to choose commands, to start programs, and to see lists of files and other options by pointing to icons and lists of menu items on the screen. Choices can generally be activated either with the keyboard or a mouse. The ArcView GUI consists of controls called menus, buttons, and tools arranged in three bars at the top of an Application window. The following figure shows the GUI associated to the called View Window : Work Site Alliance Community Based GIS Education 4

5 Figure 1.2. Basic Graphical User Interface of ArcView. The Menu bar provides access to ArcView operations through pull-down menus. The Button bar provides quick access to commonly used operations. The Tool bar contains tools that perform operations requiring input from the mouse. (Also, when you click on a tool, the cursor changes to reflect the tool you have chosen). When you place the cursor over a menu choice, button, or tool, the Status bar displays a one-line description of the operation it performs. The Status bar also reports measurements and displays a progress bar for lengthy operations. (ESRI) Below are examples of ArcView sessions showing all the available types of documents in a GIS project. View document Table document Chart document Layout document Script document Project A project is a collection of associated windows, or documents, that are displayed during an ArcView session. The Project window contains all of the other documents associated with the project (views, tables, charts, layouts and scripts). All of these associated documents are accessed through the active project window. Projects are text (ASCII) files stored with an.apr extension. Projects contain pointers to the physical locations of associated documents as well as user preferences (colors, GUI, window sizes & positions). The user preferences stored with the project affect only the way the data is displayed not the data itself. Work Site Alliance Community Based GIS Education 5

6 View Figure 1.3. Project window containing associated ArcView documents. A view is the graphic representation of spatial information and can contain any number of layers or themes of spatial information (see Chapter 4). The different themes associated to a view are listed in the Table of Contents, a sizable space located along the left side of the View window. As seen in the example below, Major Roads, Schools, and Census Block Groups polygons would be the selected themes in a single view. Table Figure 1.4. View window displaying layers or themes of spatial information. A table is ArcView s representation of tabular data. Tables contain descriptive information about a specific subject. Each row, or record, defines one entry in the database (e.g., one Census Block polygon); each column, or field, defines a single characteristic for the entry (e.g. Area). Any dbase, INFO or ASCII file can be displayed as an ArcView Table (see Chapter 2). Work Site Alliance Community Based GIS Education 6

7 Figure 1.5. Table displaying tabular data about the theme. Chart Charts provide graphic representation of summarized tabular data. Charts can also query data from the table from which it was built. Six chart types are available: line, bar, column, X,Yscatter, area, and pie. (NOTE: the same chart types as in the Microsoft Excel spreadsheet software). The example below depicts GIS data of high school sizes on a bar graph. Layout Figure 1.6. A chart summarizing tabular data. The layout document is used to combine all other documents (views, tables, and charts) into an output document (usually a hardcopy map). Any previously composed view can be placed into a layout. Within the layout a north arrow, scale bar, legend and other graphics can be added (see Chapter 6). Work Site Alliance Community Based GIS Education 7

8 Figure 1.7. A layout combining views, tables, and charts for map-making purposes. Script Script windows are for writing and displaying Avenue scripts that customize the ArcView user interface or perform user-designed tasks. From the button bar you check syntax, debug, and run your script. Avenue is ArcView s object-oriented programming language. With Avenue you can modify the appearance of ArcView, create new programs, make complex tasks simple, and communicate with other applications such as ARC/INFO, a relational database manager or a spreadsheet. Using scripts, ArcView can be customized for specific user needs and for specific applications and tasks. The figure below is an example of the Avenue scripting language. Figure 1.8. Example of the object-oriented programming language used by ArcView. Work Site Alliance Community Based GIS Education 8

9 Exercises In this section, the student will learn to open ArcView projects and themes, and use some of the buttons and tools associated to the View document. 1A. Opening a Project in ArcView GIS From the Start menu, go to Programs. Open the GIS application that is installed on your computer (with the same steps as if you have to open any other application such as Microsoft Word, etc). When ArcView is opened, you will notice an Untitled Project window with the following dialog boxes: Click on OK in the first dialog box (on the left of the page). Click on No when the second dialog box pops up, and an empty view window will open. Work Site Alliance Community Based GIS Education 9

10 1B. Adding Themes to a View With the View window open and active, you then add a theme to the view. Click on the Add Theme button. An Add Theme window pops up. After navigating to the right path (Your Drive:\Chapter 1\data), the Add Theme window will appear as follows. NOTE: When you choose to add a theme to a project, it may be from: a Feature Data Source (ArcView shape file, ARC/INFO coverage) an Image Data Source (Digital Photos, etc) In this exercise, we will deal only with Feature Data. You can choose to add one or multiple themes. To do this hold the Shift Key down (for multiple selection), and click on the themes: Detroit.shp, Roadhwy.shp, and Schools.shp Click on OK. Work Site Alliance Community Based GIS Education 10

11 1C. Working in the View Window On the left side of the View window, we have the Table of Contents which holds a list of the themes in the view. Themes which are on are denoted by the check mark in the box on the left of each theme. If a theme is on, then it is visible in the view. Click on the check box for each of the three themes you have just added. The order of themes within the Table of Contents dictates the order in which the themes are drawn in the view. The top theme in the Table of Contents is drawn last and is the top layer of the view. The order of the themes can be rearranged by clicking on a theme with the mouse and then dragging it to a new position in the Table of Contents. Notice the order in which the themes are in your View Window. Click on and drag the Detroit.shp to the top of the Table of Contents. Notice the change in the map by interchanging the order of the themes as directed. Drag the theme Detroit.shp back to the bottom list. Many functions in ArcView require that one or more themes are active. An active theme is that which responds to the View GUI. The legend for an active theme appears raised in the table of contents. Themes can be made active by clicking on the name of the theme in the Table of Contents. Multiple themes may be made active by holding down the Shift Key and clicking with the mouse on each required theme. Make the Detroit.shp theme active. Click on the Zoom to Active Theme button. Work Site Alliance Community Based GIS Education 11

12 1D. Using Some Buttons & Tools in the View GUI: Another strength of ArcView is the additional tools associated with the View window. These tools can be used on themes and can help you manipulate the view, find features in the themes, and add graphic features. Click on these buttons for immediate response. Zoom to extent of all themes Zoom to extent of active themes Zoom in Zoom out Click on the following tools and move the pointer into the view graphics area. Zoom into view (single click, or click and drag a box in the view) Zoom out from view (single click in the view) Move the view around (click and drag in the view) Click on the Select Features tool. Move the pointer to the polygon located in the middle of the Detroit.shp theme (which should be the active theme). The polygon is now selected, and become highlighted. Click on the Zoom to Extent of Selected Features button. The View will focus on the selected polygon. Click on the Clear Selected Features button to un-select the previous area. Work Site Alliance Community Based GIS Education 12

13 Click on the Zoom to Previous Extent button to retrieve the previous aspect of the view. Additional feature theme functions include the Identify Feature tools. Find Feature, and the The find feature button allows you to find a particular feature in a view, table or chart. In a view all the themes you want to search should be active. The string (text or numeric) you wish to search for is typed in the dialog box. This provides a search of any occurrences within the project window. Make the Schools.shp theme active. Click on the Find Feature tool. A dialog box pops up. Type in Denby HS. Click OK. The High School location is highlighted in the View. 1E. Closing the Project Go to the Project window. From the File menu, choose Close Project. Click on No when prompted to save the changes you made so far. Work Site Alliance Community Based GIS Education 13

14 Bibliography Davis, Bruce E. GIS: A Visual Approach. Santa Fe: Onward Press, ESRI Web Page. Environmental Systems Research Institute, Inc. Lakhan, V. C. Introductory Geographical Information Systems. Chelsea: Summit Press, Work Site Alliance Community Based GIS Education 14