A digital elevation model (DEM) is a raster dataset in which every cell holds an elevation value, representing the height of the Earth’s surface across an area. It is the general term for digital height data, and in practice is used as an umbrella covering both the digital surface model (DSM) and the digital terrain model (DTM).
DEM, DSM and DTM are not interchangeable
This is the most common source of confusion in elevation data, and choosing the wrong one produces quietly wrong answers.
- DSM — includes everything on the surface: buildings, tree canopy, infrastructure.
- DTM — bare earth, with those objects removed.
- DEM — the generic term, which may mean either depending on the provider.
Because DEM is ambiguous, always check which the supplier actually means before using it.
How DEMs are produced
Common sources are LiDAR, photogrammetry from aerial or satellite imagery, and radar interferometry. Each carries different vertical accuracy and resolution, and the cell size of the raster sets the finest detail the model can express.
What they are used for
Elevation data supports flood and drainage modelling, line-of-sight and telecoms planning, slope and terrain analysis, viewshed calculation, and infrastructure design. In location analytics it also informs how signals propagate and where physical barriers shape how people actually move.
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