Geographic Information SystemsScott WiegalMitchell MathewsDr. Rene ReitsmaBA 471 May 9, 20060AbstractGeographic Information Systems (GIS) have opened doors to a whole new way offinding and displaying information. They combine geographic and descriptive information on a type of visual mapping that gives the descriptive information a relationship based on geography. The creation of GIS computer programs has found a growing industry with several competitors. Most notable are IDRISI, GRASS, and several systems offered by ESRI which all have unique product offerings that take different approaches towards GIS. The two types of systems in which GIS are stored and displayed are Vector and Raster. While they differ from one another, each has its own use depending on the information being processed. IntroductionGIS has many users these days, from government to private businesses, and corporations to individual users. GIS can be found in everyday use such as Mapquest or in large projects requiring satellite imagery. People seem to be intimated at first by the technical nature of GIS, but once understood it stands to help anyone interested in findinggeographic relationships between their variables. Some people may not have thought of combining their databases in such a manner before and at first might not see a use for it. After this report the reader should have a better understanding of what GIS is and how others have used it.1What is GIS?Information in the past was limited to spreadsheets and databases, however it nowhas the chance to be presented in combination with geography. GIS is unique in the way it uses spatial information in its displays. Webster dictionary defines spatial as, “relating to, occupying, or having the character of space. (1)” GIS allows the linking of descriptive information with geographic information, presenting a more effective and easier to interpret result. Multiple layers of descriptive information can be applied to the same geographic mapping, allowing those interested to find relationships between the types of information. An insurance company can use this when calculating how much of a premium to charge on a house. Many variables could be used in relation to the house; property value (descriptive), previous claims on the house (descriptive), previous claims in the neighborhood (spatial & descriptive), proximity to police and fire station (spatial). The extent that insurance companies use GIS is not limited to these, but rather this shouldhelp give some insight into how the different variables can be used in conjunction to answer a question.GIS can be viewed in three ways; database view, map view, and model view. Database views have the most obvious blend of descriptive and geographic information as attributes of interest are assigned values across a geographic map. Map views show physical features of the earth’s surface and help track a desired question. Mapquest is a good example of this as it takes a geographic map and plots a path through it. The modeling view is the most abstract of the three as there is not a geographic map shown. 2Rather, it does as it’s name implies and models the data by turning geographic features into a descriptive trait. All three views may be stored in either raster or vector form depending on the specifics of the project in question.Database Map Model Raster SystemThe raster system is one of two systems used in Geographic Information Systems technology. In this system, data are represented in columns and rows where each individual cell may represent a combination of various values. Raster systems use spatial data in a matrix form two dimensionally, much like a checker board. It is generally a simple tool to use. The most practical application of representing data in the raster systemis through photographs, which are referred to as raster graphs. Through raster graphs, 3data are often shown in color. Raster graphs require a relatively large amount of storage, as each individual cell contains a value and a raster image contains many individual cells.Vector SystemThe vector system is the other system used in GIS. Vector uses points, lines and polygons to represent shapes and/or objects. This system designates one color for the line and another color to represent the fill in portion. When plotting points, the quality or proportion of objects will not be affected if the resolution is changed. Vector is well suited to designate boundaries shown by traditional maps. Raster versus VectorBoth raster and vector systems have their advantages. The raster system is very good at displaying various surface features. It is ideal to use for satellite imagery becauseof the detailed nature it is able to provide. Using the raster system allows for easy implementation of overlays, which in a vector system can become more difficult. If you are working with a limited amount of storage space, a vector system is the most beneficial. With the capabilities of indefinite zoom you are able to enlarge an area while 4preserving the quality and proportion of information. Using vector allows the user to have more accurate measurements through the use of (x,y) coordinates.Systems used in GISOne system used in GIS is the IDRISI system. IDRISI is a raster system that was developed at the Graduate School of Geography at Clark University. It is supported by a non-profit organization called the IDRISI Project and is the most widely-used raster GIS system in the world. IDRISI provides a professional level of work at a price that is affordable to many people. It does not require a high degree of knowledge to operate and can be used on multiple platforms. IDRISI is not an acronym, it was named after a North African cartographer and geographer of the twelfth century whose work was referenced over the next 500 years.Geographic Resources Analysis Support System, or GRASS, is an open source GIS system. It was originally developed by the U.S. Army Construction Engineering Research Laboratories as a land management and environmental planning tool. GRASS isable to support both vector and raster applications. It is currently used in educational and commercial enterprises. Governmental agencies are also taking advantage of the benefits that GRASS is able to provide.ESRI offers one of the most commonly used vector programs, called ArcGis. ESRI has desktop, server, and mobile applications, offering a full service package for whatever GIS needs a professional may
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