G&ES 391: A course in the department of Geography & Environmental Studies at Northeastern Illinois University, Chicago

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What's GIS
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Web_Authoring
Maps/Printing
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Importing
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Tables
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Raster and vector are the two main categories of GIS programs. One uses pixels and the other uses points, lines and polygons to represent spatial features.

Types of GIS Programs

There are many different GIS programs, some of which have special purposes. Generally, we can categorize GIS into what are called "raster" and "vector" programs. Raster GIS generally incorporates one attribute value -- say, land use or soil type -- into each pixel of what you might think of as a large bitmap image. Each value of the attribute may be assigned a different color, so the coverage appears to be a map, typically, or a photograph. Remotely sensed information, by plane or satellite, is easily incorporated into a raster coverage. ERDAS, IDRISI and ArcGrid are raster GIS programs.

The other family of programs, the "vector" GISs, contain actual points, lines and areas, similar to a CAD drawing or something from Adobe Illustrator. Each of these objects is connected, in effect, to an entire row of a spreadsheet of data, which contains any number of columns. Each column is the variable, each row is the object (e.g., tree), and each cell of the spreadsheet is the value of that variable for that object. ArcView, ArcGIS, ArcInfo, Maptitude, TransCad, MapInfo, and Manifold are examples of vector GIS programs.

Beyond the spatial units and the data complexity, there are many similarities between raster and vector GIS. Raster is often used when the information in question is collected remotely, e.g., by satellite; and vector is typically better for survey data, demographic information, economic data, and things which can not be "seen" on the landscape from a distance. Even so, there is a great deal of cross-over and these two families are merging, slowly, with technological advances.

It might be useful to know that while most GIS programs are proprietary, there are good programs which are "open source," or in the public domain. They are being developed in a grassroots, modular way and represent a dynamic arm of the GIS revolution. GRASS (raster/vector) and MapServer (primarily vector) are two examples of open source GIS.