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Hillside polygon from DEM

02-03-2021 09:38 AM
New Contributor II

I have a DEM that covers a large area of steep hills. My end goal is to have a base layer of the entire area (raster or polygon) that identifies the hilltops (areas above where the hills begin to heavily slope), the hillsides (areas where the hills slope at their greatest (say 30+%) and areas below the base of the hill line where slopes are gentler.

I have been playing with the slope tool in spatial analyst, however I have some problems. First, the slopes gradually diminish as you get to the upper reaches of the canyons, so I do not have a way to connect the sloping areas around those lower slopes at the upper reaches to create a dividing line between hilltop and valley. Second, the area covered is large enough that the elevations of the base of the hill lines in the eastern portion of the DEM are actually found on the upper side of the hills in the western portion of the DEM, so I cannot identify a solid elevation level to establish the line. Third, I can't figure a way to separate the hilltops (above the heavily sloped area) from the valley (areas below the heavily sloped area) based solely on slope because both those areas contain similar ranges in slope.

Any advise is appreciated. For reference I have access to the basic license and I have spatial analyst.

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