

Digital Elevation Model (DEM) - A file with terrain elevations
recorded at regular intervals on a fine-grained grid and 
organized by USGS quadrangle; the \digital\ equivalent of the
elevation data on a \topographic map\.  Currently available at
two different \resolutions\; 1-degree DEM have a resolution of
roughly 100 meters and are produced from \DMA\ \DTED-1\ elevation
data, while 7.5 minute DEM have a resolution of roughly 30 meters
and are produced from contour \overlays\ or NHAP quad-centered
photographs.
