DEMsDTMsDSMs

DEMs, DTMs, and DSMs are three related types of gridded elevation data used in geographic information systems, remote sensing, and spatial analysis. They provide three-dimensional representations of surfaces and are foundational for terrain analysis, hydrology, urban planning, and environmental monitoring. While they share a common origin in elevation data, each model emphasizes a different surface characteristic.

A digital elevation model, or DEM, is a raster grid of elevation values representing the surface of the Earth in a broad sense. In practice, the term is sometimes used interchangeably with DTMs or DSMs, but it is often intended to denote a general elevation surface. The exact interpretation can vary by organization, so definitions should be specified in any data product.

A digital surface model, or DSM, represents the elevation of the first visible surface above the ground, including natural and man-made features such as trees, buildings, and bridges. DSMs are useful for line-of-sight analysis, telecommunications planning, urban studies, and canopy height estimation when combined with other data.

A digital terrain model, or DTM, focuses on the bare-earth surface, removing vegetation, buildings, and other objects. DTMs are commonly used for hydrological modeling, flood risk assessment, slope and aspect analysis, and geomorphology because they reflect the terrain without above-ground obstructions.

Common data sources include LiDAR, stereo photogrammetry, and radar; processing workflows often derive DTMs by filtering out non-ground returns to create bare-earth surfaces, while DSMs may retain or interpolate surfaces corresponding to canopy or built structures. Formats such as GeoTIFF, IMG, and ASCII grids are typical, with resolutions ranging from sub-meter to several meters.