A 3D representation of terrain surface elevation data, typically stored as a raster grid. DEMs are foundational datasets for hydrological modeling, watershed delineation, and flood mapping.
A Digital Elevation Model (DEM) is a gridded representation of the Earth's bare-earth surface, where each cell contains an elevation value referenced to a vertical datum. DEMs are created from various sources including LiDAR, photogrammetry, radar interferometry (InSAR), and satellite stereo imagery. In hydrology, DEMs are essential for delineating watersheds, calculating flow direction and accumulation, estimating slope and aspect, and modeling surface runoff pathways. Common global DEM products include SRTM (30 m and 90 m resolution), ASTER GDEM (30 m), and Copernicus DEM (30 m). Higher-resolution DEMs (1-3 m) derived from LiDAR are increasingly available for detailed floodplain mapping and urban hydrology. The accuracy of hydrological analyses is highly sensitive to DEM resolution and quality, particularly in flat terrain where small elevation errors can significantly alter predicted flow paths. DEMs are distinct from Digital Surface Models (DSMs), which include vegetation and structures above the bare earth.