DEM vs DSM vs DTM: What's the Difference?
DEM, DSM and DTM sound alike and are often used interchangeably, but they describe different surfaces. Getting them straight matters, because using the wrong one can put real error into a volume or a drainage plan.
DSM — Digital Surface Model
A DSM captures the top of everything on the ground: bare terrain plus buildings, trees, vehicles and other objects. It is usually what you get first from photogrammetry or LiDAR, because sensors see the top surface.
Use a DSM when the objects matter — line-of-sight over rooftops and canopy, volumes of piles and structures, or urban and forestry work.
DTM — Digital Terrain Model
A DTM is the bare-earth surface with buildings and vegetation removed. It represents the ground itself, which is what most engineering work references.
Use a DTM for earthworks, cut/fill, grading, drainage and contours — anything that should follow the terrain rather than the objects sitting on it.
DEM — the general term
"DEM" (Digital Elevation Model) is commonly used as an umbrella term for a gridded elevation model, which may be either bare-earth or surface depending on how it was produced.
When precision matters, say DSM or DTM. When you just mean "a grid of elevations", DEM is fine.
A quick way to remember it
DSM = surface (with objects). DTM = terrain (bare earth). DEM = the general elevation grid. If someone hands you a "DEM", it is worth asking which one they mean before you compute a volume with it.
Open DEMs, DSMs and DTMs in STREAM
Native Windows · fully offline · free beta