DEMgegevens

DEMgegevens are digital representations of the Earth's surface elevations. A Digital Elevation Model (DEM) stores terrain heights in a regular grid, with each cell containing the elevation of the ground surface relative to a vertical reference datum. DEM data are used in mapping, hydrological modelling, flood risk assessments, land-use planning, and 3D visualization. It is important to distinguish DEM from Digital Surface Model (DSM), which includes buildings and vegetation, and from Digital Terrain Model (DTM), which represents bare-earth elevations similar to a DEM.

Vertical and horizontal references: Elevation values are tied to a vertical datum such as a national orthometric datum or an ellipsoidal reference; horizontal coordinates are given in a specific projection and datum. The choice of datum affects the interpretation of heights and positions, so users must ensure compatibility with other geodata.

Sources and methods: DEM data are produced by airborne LiDAR, photogrammetry, radar (InSAR), or bathymetric sonar, and can be generated from stereo imagery. LiDAR-based DEMs offer high resolution and accuracy, often at 1 meter or finer in urban areas; coarser DEMs use 5–30 meter grids.

Formats and access: Common file formats include GeoTIFF, ASCII GRID, IMG, and NetCDF, while the underlying data may be stored as point clouds in LAS/LAZ formats. In the Netherlands, AHN data are published through PDOK and open data portals, frequently under open licenses for many uses.

Applications: DEMgegevens support flood modelling, watershed analysis, drainage planning, road and railway design, suitability analysis, and 3D landscape visualizations.

Limitations: Elevation values may contain voids or errors in forested or coastal areas; resolution limits detail; vertical accuracy depends on data source and processing.