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GRASS Help System |
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.