Understanding Slope and Aspect
Slope is the rate of change of elevation at each point — how steep the ground is; aspect is the compass direction a slope faces. Together they are two of the most useful things you can derive from a DEM, turning 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.
Frequently asked questions
What is slope in terrain analysis?
Slope is the rate of change of elevation at each point — how steep the ground is — usually shown in degrees or as a percentage on a colour scale from flat to steep.
What is aspect in terrain analysis?
Aspect is the compass direction a slope faces — north, east, south or west — which controls how much sun a hillside receives and how exposed it is to wind and weather.
Why do slope and aspect matter?
Slope drives decisions about buildable ground, road grades, erosion risk, machine access and safety, while aspect matters for agriculture, solar siting, snowmelt and habitat, where orientation changes the outcome as much as steepness does.
Where do slope and aspect data come from?
Slope and aspect are computed directly from a DEM by comparing each cell to its neighbours, and are usually shown as colour overlays on the terrain that reveal patterns raw elevation hides.
Sources
Run slope and aspect analysis in STREAM
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