Digital Elevation Models and Terrain Data

A Digital Elevation Model (DEM) is a raster grid in which each cell stores a single elevation value sampled at a regular horizontal interval, providing the base dataset from which slope, aspect, hillshade, and hydrological layers are derived. Practitioners distinguish a Digital Terrain Model (DTM), which represents the bare-earth ground surface with vegetation and structures removed, from a Digital Surface Model (DSM), which instead records the first reflective surface encountered, including tree canopies and rooftops — a distinction that matters directly for tasks such as line-of-sight analysis, forest canopy height estimation, or flood modeling, where using a DSM in place of a DTM can introduce meter-scale errors. Elevation data is most commonly distributed as GeoTIFF rasters, but an alternative structure, the Triangulated Irregular Network (TIN), stores elevation at an irregular set of points connected into a mesh of non-overlapping triangles via Delaunay triangulation, allowing denser sampling along breaklines such as ridges, cliffs, and stream channels while using far fewer points in flat, featureless terrain than an equivalent uniform raster would require.