Digital Elevation Model — a raster dataset representing the elevation of the Earth's surface at regular grid intervals.
A DEM stores elevation values as a grid of cells, where each cell contains the height above sea level for that location. DEMs are used to model terrain, calculate slopes and aspects, delineate watersheds, and support flood risk analysis.
There are two common types: a Digital Terrain Model (DTM) represents the bare ground surface; a Digital Surface Model (DSM) includes the tops of buildings, trees, and other objects above the ground.
Example: Natural Resources Canada provides a national DEM at 20-metre resolution. A hydrologist uses it to model how water flows across a watershed — the DEM's elevation values determine which direction water drains from each cell, enabling the delineation of drainage basins.
LiDAR surveys produce high-resolution DEMs that are increasingly available as open data from provincial and municipal governments across Canada.