Understanding Slope and Aspect
Slope and aspect are two of the most useful things you can derive from a DEM. They turn raw elevation into information you can act on — where it is too steep to build, which hillsides get the sun, where water will run.
Slope: how steep
Slope is the rate of change of elevation at each point — how steep the ground is. It is usually shown in degrees or as a percentage, on a colour scale from flat to steep.
It drives decisions everywhere: buildable ground, road grades, erosion risk, machine access and safety.
Aspect: which way it faces
Aspect is the compass direction a slope faces — north, east, south or west. It is what controls how much sun a hillside receives and how exposed it is to wind and weather.
Aspect matters for agriculture, solar siting, snowmelt and habitat, where orientation changes the outcome as much as steepness does.
Both come from the DEM
Slope and aspect are computed directly from the DEM by comparing each cell to its neighbours. Shown as colour overlays on the terrain, they reveal patterns that raw elevation hides.
Run slope and aspect analysis in STREAM
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