Glossary for Geospatial Science

DEM:Digital Elevation Model.� (Also DTM, �Digital Terrain Model�).� A computerized representation of an elevation surface.� Specifically, a raster in which the value in each cell represents the surface elevation at that location in the scene.� DEMs are USGS geographic elevation data distributed in raster form on open reel magnetic tapes.� There are 2 basic types:� 1) The DMA type created by the Defense Mapping Agency in both a fixed cell size and a 3 x 3 arcsecond cell size distributed in 1 x 1 degree files.� 2) A newer format for those 7.5' USGS quadrangles that have been processed into 1 x 1 arcsecond elevation cells.