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  • A Brief Introduction to GIS

    by John Regan

    A Geographic Information System (GIS) is one of the best tools currently available for managing geographic information. It is estimated that about 85% of the information managed by cities and counties is geographically referenced in some way, such as the location of a building shown on a map. Examples of geographic information are addresses, parcels, district boundaries, the spatial distribution of health statistics, roads, washes, buildings, and utility locations.

    The definition of GIS varies depending on specific applications, but generally it is described as a computer-based system with the ability to store, retrieve, modify, analyze, and represent geographic data as useful information.

    A GIS can be useful for relating mapped features and their attributes (non-graphic information associated with features) in two ways. First, the actual feature from a map, a sewer manhole for example, displayed on a computer screen may be pointed at electronically and used to access and display all of the attributes contained in the computer's database regarding that feature - the year it was installed, its material, diameter and capacity, etc. Second, the database itself can be queried to display only those features selected in a way which may give it meaning. An example of this is choosing all parcels of land selling for between fifty to sixty thousand dollars in the last year, delineating the areas where the highest rate of real estate transactions occurred in that price range.

    Many government agencies are utilizing GIS because it offers a way of understanding and dealing with complex spatial problems by organizing the data, viewing their spatial associations, performing multiple analyses, and synthesizing results into maps and reports.

    GIS technology is very useful, allowing the public and many different departments access to the same basemaps and database. This means that each department does not have to keep separate versions of other department's maps and data in order to use them for their own agency's needs. Features or attributes need to be modified and updated on only one basemap and database and then be shared by everyone. Departments can portray mapped information at whatever scale they require, using the colors or symbols they want and accompany the maps with text and reports tailored to meet their needs.

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