Geographic information systems (GIS) are systems of computer hardware, attendant software, and digitized spatial data combined for the purpose of storing and subsequently displaying the spatial data in a cartographic format. GIS thus graphically display the spatial relationship that exists between various features of the earth's physical and cultural landscape. The study and understanding of these spatial relationships is the essence of the discipline of geography. The spatial relationships of these landscape features influence a plethora of human endeavors from city planning to retail store locations to environmental awareness.
Landscape features exist in time and place and exert influence over one another. Physical features of the landscape include such things as streams, topography, glacial deposits, ground cover, swamps, deserts, and soil types. Cultural features are man-made and may have a physical reality (such as towns, roads, sewer lines, and housing) or a symbolic reality (such as political boundaries and land parcel dimensions). There is a constant interplay between these landscape features. For example, topography and underground springs influence the course of streams and creeks that run downhill to comingle and form rivers. Using a river as part of a transportation network, people settle on its banks and a town begins to evolve. An entrepreneur buys a piece of riverfront property, has it surveyed and registered, and erects a dock and a warehouse. A railroad builds a bridge over the river and a spur line adjacent to the warehouse. An understanding of this milieu is incomplete without an understanding of the influence these features and activities have on one another.
Information relating to such scenarios as the one above can be collected, digitized, and stored in a database. Geographic information systems allow an operator to display this digitized spatial information as a map.
Maps are generally regarded as the most efficient way of communicating spatial information. The value of GIS lies in its ability to quickly overlay a base map—such as that of a city, county, or subdivision—with layers or combinations of data. For instance, a township map can be overlaid with demographic data from the U.S. Bureau of the Census relating to the racial characteristics of its neighborhoods. This map can then be overlaid again with data from the U.S. Environmental Protection Agency showing the location of polluted or contaminated sites. The operator would then have a graphic, visual correlation between race and contaminated sites in the township. After printing the map or storing it as a computer file the demographic data can be removed and replaced with data reflecting the location of wells, providing a second correlation—one between contaminated sites and drinking water. This is the value of GIS, the ability to efficiently manipulate and display spatial data in its most effective manner of presentation—a map.
Like most other computer operations, the advantage of geographic information systems are their speed and efficiency. Maps of course have been drawn and produced for centuries and overlays can be made with sheets of polyester film. With GIS, however, the overlays can be removed or added very quickly. Another key advantage of GIS is the ability to store and integrate data. GIS can take information from such diverse formats as satellite imagery, air pollution analysis, and census statistics and integrate it into a meaningful whole.
When geographic information systems began being introduced in the 1980s, they found immediate favor with local government agencies and still remain a popular tool for them. All local government agencies are unique but they also have common characteristics that provide a framework for GIS use. In a nonscientific telephone poll of local government agencies in the state of Washington, the Municipal Research Services Center found GIS being used for the following applications, among others: refuse collection, zoning, maps for distribution at public hearings, storm water control, utility customer service, walking trails, water pipes, sewer systems, land use, permit tracking, wetlands inventory, environmental analysis, police patrols, land parcel description, boundary description, topographic mapping, emergency services, buffer zone description for adult entertainment establishments, and location of manholes. The software used by these agencies was either ArcInfo, Arc View, ArcCAD or AutoCAD; hardware was either PCs with Pentium processors or Unix workstations.
Geographic information systems gradually found favor in the business world and are now an integral part of many business operations. One GIS proponent claims that this technology makes the business world visible by converting its "hills and valleys"—such as customers, market areas, suppliers, and sales territories—into meaningful data that can be analyzed and visualized. Geographic information systems have rapidly expanded into most areas of business that have spatial dimensions, such as banking (e.g., mortgage lending, branch locations) and retailing (e.g., service areas, store locations).
[ Michael Knes ]
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U.S. Department of the Interior. U.S. Geological Survey. "Geographic Information Systems." Reston, VA: U.S. Geological Survey, 1997. Available from info.er.usgs.gov/research/gis/title.html .