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Geographic information systems Geographic information systemsGeographic information systems (GIS) are at the forefront of the mapping revolution. A GIS makes it possible to combine layers of digital data from different sources and to manipulate and analyze how the different layers relate to each other.With a GIS, researchers can combine geographically referenced data from the NDCDB and many other sources and perform complex analyses that have not been possible before. GIS's are being used in applications as varied as:Soil conservation.. The Department of Agriculture is combining DLG information with scanned photographs and field boundary data to report and analyze soil use.Crime solving.. Police investigators link police record systems with geographic information to analyze crime patterns and help solve cases.Emergency response planning. A GIS can be used to combine transportation and earth science information to help plan emergency response to a natural disaster, such as an earthquake. By merging information on the types of roads, locations of fire stations, and locations of faults, the anticipated response times of fire and rescue squads can be calculated both under normal conditions and following transportation blockages caused by an earthquake.Marketing. Merging sales information with digital map data can help companies target markets or present sales information in geographic terms.Whether used in government, business, military, or a host of other applications, a GIS provides the means to examine relationships in ways never before possible. Satellite images of San Mateo County, California, have been combined in a computer with elevation data of the same area to produce this perspective view. Where do we go from here?With today's technology, it is possible to generate personal maps on a home computer. In the near future, traffic jams may be avoided with dashboard-mounted computer mapping systems. Beyond that may lie interactive television where local news or weather reports can be chosen by touching a map on the screen.Digital techniques will continue to influence mapmaking, enabling more rapid production of accurate, current maps. Computers can also help us manipulate data derived from traditional maps in increasingly sophisticated ways.| Top | Main Table of Contents | Geography Publications | Eastern Region Geography | Geography Home | This online edition contains full text from the original publication. This document has undergone official review and approval for publications established by the National Mapping Division, U.S. Geological Survey. Some figures have been modified, added or deleted to improve the scientific visualization of information.
The Digital Mapping Revolution The Digital Mapping RevolutionComputer technology will not only change the way maps are made but how they are used.Computer-assisted map production is making it easier to produce new paper maps and to revise existing ones. The USGS is responding with innovative ways of compiling map data and using them for map production. Many of the mapmaking processes described above are being changed or eliminated. Improved efficiencies in most facets of production will shorten the 4 to 5 years it takes to produce a map by traditional methods.Widespread acceptance of computers and related technologies has accelerated the demand for mapping information in computer-compatible form. Government agencies and private businesses now require digital mapping information for their computer-based systems.The goal of the USGS is to stay in the forefront of the technology that will modernize the production of traditional maps while responding to the growing need for data in digital form.|| Top || Digitizing dataMost of the USGS's digital map data are collected from existing topographic maps. The task is monumental.Map digitization resembles the original map scribing process in that it requires that each feature on each map separate be located, classified, and traced. A map can have 10 or more different layers--roads, contours, boundaries, surface cover, and manmade features, for example--that require digitization. Maps can be digitized by hand, tracing each map's lines with a cursor, or automatically with scanners.After digitizing, several editing operations remain. For example, attribute codes must be added to identify what each digitized line or symbol represents. A variety of other tasks must be performed to ensure that information is complete and correct, including matching features with adjoining files, matching features relative to each other within the file, and controlling the accuracy of attribute coding and positions.The National Digital Cartographic Data BaseThe USGS is the principal agency developing standards and coordinating other matters related to Federal digital cartographic data. The National Digital Cartographic Data Base (NDCDB) was established by the USGS to distribute digital data that meet these standards for use in map production and in automated systems.NDCDB data provide a framework of reference for other data about the Earth and its resources. The NDCDB data consists of digital line graphs ( DLG) and digital elevation models ( DEM). DLG's are the digital representation of information typically found on a topographic map (point locations, lines and area outlines). DEM's are matrices of elevations for ground points spaced at regular distances.Nationwide DLG coverage is complete for transportaion and hydrographic features found on 1:100,000-scale maps and for most information found on 1:2,000,000-scale maps. The 1:100,000-scale data served as the base for the Bureau of the Census Topologically Integrated Geographically Encoded Reference files--the digital representation of the Nation used in the 1990 census.|| Top ||
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