What is a digital elevation model (DEM)?

A DEM (Digital Elevation Model) is a raster where each cell holds an elevation value above a reference level (usually NAP in the Netherlands). It represents terrain relief as a grid, not as loose elevation points.

Applications: slope and aspect, flow direction, flood models, 3D display with orthophoto draped on DEM, viewsheds. PDOK and Rijkswaterstaat deliver elevation models; resolution varies from decimeters (AHN) to meters.

A DEM is not an orthophoto (color image) or vector contours alone — though contours can be derived from DEM. DSM includes buildings and vegetation; DTM is often ground surface only.