US Geological Data: Digital Line Graphs from 1:100,000-Scale Maps. Data Users Guide 2

摘要

The National Cartographic Information Center (NCIC) distributes digital cartographic/geographic data files produced by the U.S. Geological Survey (USGS) as part of the National Mapping Program. Digital cartographic data files may be grouped into four basic types. The first of these, called a digital line graph (DLG), is line map information in digital form. The second form, called a digital elevation model (DEM), consists of a sampled array of elevations for ground positions. The third type is land use and land cover digital data which provides information on nine major classes of land use such as urban, agricultural, or forest. The fourth type, the Geographic Names Information System, provides primary information for known places, features, and areas in the United States identified by a proper name.