# Calculate Average Slope over Specific Distance [closed]

I'm working with a development ordinance in which building cannot occur on areas where the average slope over a 50 foot distance exceeds 12% and these areas need to be mapped.

Calculating and categorizing the >12% areas on the DEM or CAD surface is straightforward, however it's determining where the 50' rolling average slope tapers to less than 12% that I'm having trouble with.

For example, if a 43-foot run with a slope of 5% steepens into a 7-foot run with 58% slope, this entire area along this 50 feet is considered a no-build area because the average is 12.2%.

I have the ability to work in QGIS, GRASS, SAGA, ArcGIS 10.3, or Civil 3D but I just don't know the workflow.

## closed as too broad by PolyGeo♦Mar 18 '17 at 5:18

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• Please try one of those products and then ask about where you get stuck. – PolyGeo Mar 18 '17 at 5:19
• Which are units (feet?), projection and DEM resolution? – xunilk Mar 18 '17 at 8:35
• NAD83 UTM Zone 15N; 1 meter DEM. I understand this has unfortunately been put on hold until the question is revised. – WOMPStation Mar 20 '17 at 21:37