The 7.5-minute Digital Elevation Model (DEM) data files are
digital representations of cartographic information in a raster
form. DEMs consist of a sampled array of elevations for a number
of ground positions at regularly spaced intervals. These digital
cartographic/geographic data files are produced by the U.S.
Geological Survey (USGS) as part of the National Mapping
Program. DEM data for 7.5-minute units correspond to the USGS
7.5-minute topographic quadrangle map series for all of the
United States and its territories except Alaska. Each 7.5-minute
DEM is based on 30- by 30-meter data spacing with the Universal
Transverse Mercator UTM projection. Each 7.5- by 7.5-minute
block provides the same coverage as the standard USGS 7.5-minute
map series. The 7.5-min USGS DEMs have been converted from the
SDTS format to the native DEM format using the corrected
SDTS2DEM conversion software produced by Dr. Gregg Townsend of
the University of Arizona. The 7.5-min USGS DEMs are the
corrected files produced by the USGS