Digital Data and Geographic Information Systems

On a planet of finite resources faced with mounting population pressures, geographic information systems already have become indispensable for resource management, policy assessments, and strategic decisions.

CONGRESSMAN GEORGE E. BROWN
Chairman, House Science, Space, and Technology Committee quoted in GISDEX Express, 1992

During the past decade, a revolution has drastically altered the nature of cartography. Beginning with efforts to automate merely the production of standard map products through the use of various computer technologies, a new industry evolved known as geographic information systems (GIS) that encompassed such processes as automated cartography, remote sensing from earth-orbiting satellites, and the sophisticated analysis of geographic information. Now the emphasis is on varied uses of geographic information in digital forms. In this environment, maps are frequently viewed as merely one of a wide variety of potential products. It is anticipated that by the turn of the century many of the products that are now published in paper form, such as topographic maps and nautical charts, will be produced electronically instead.

Computer-generated map of Dade County, Florida, showing the extent of damage caused by Hurricane Andrew, August 22, 1992. This map was produced by Metro-Dade using ArcView, a sophisticated geographic information system developed by Environmental Systems Research Institute, Inc. (ESRI). (Environmental Systems Research Institute, Inc. Collection)

GIS treats data as different layers. For example, one layer may contain the street pattern of a city, another the administrative districts of the city, and a third might show the location of reported crimes. Within a GIS, the portrayal of each type of data can be tailored to meet specific criteria, and then the various layers combined to form a single map. One of the key features of a GIS is that any type of information with a geographic component can be mapped. Thus, thematic maps can be constructed from layers of data that represent traditional cartographic information and from data sets that the user supplies from other sources.

Some of the most important developments in GIS to date have come from the federal government. Probably the most significant is the Topological Integrated Geographic Encoding Reference (TIGER)/Line Census File developed for the 1990 census by the Bureau of the Census. The TIGER/Line Census File was created to describe the administrative units by which data for the 1990 decennial census would be collected and analyzed. It depicts most highways, railroads, streams, and administrative boundaries in the country. Because this file represents a basic seamless electronic map of the country, it has been adopted as the foundation of many GIS applications for such purposes as analyzing or controlling transportation, examining demographic patterns, or determining business locations. The TIGER/Line Census File is stored on forty-seven 3 -inch discs. Other major files include the U.S. Geological Survey Data Files and the U.S. National Cancer Institute Mapping Program.

This computer-screen map, which shows mortality statistics for white males from lung, trachea, and pleura cancers in the state of North Carolina, is representative of the more than 100 million images that can be generated from the National Cancer Institute Mapping Program. This digital data base is stored on sixteen computer discs. (U.S. National Cancer Institute Mapping Program)

Among the commercial software available are six packages produced by Environmental Systems Research Institute, Incorporated (ESRI), Redlands, California, which enable users to browse, query, and display thematic spatial data for the United States and the world at county, state, and country levels; and a package called Marine Data Sampler, designed to be used with esri's ArcView software; and Magellan Geographix, a software and data set package on fifty-six 3 -inch discs that contains more than three hundred maps of cities, countries, regions, and continents, each of which can be displayed in multiple layers of some twenty existing attributes of information or new attributes which can be added by the operator.

Political map of Europe showing national capitals and major cities as derived from Magellan Geographix digital map file. This image represents the base layers on which other layers of geographic information can be added. (Magellan Geographix Database)

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