# Calculate path which follows a given grade or grade/slope relation

How is it possible to draw a path, which follows a given grade or a trail grade / slope relation?

I know least cost path where I was able to calculate least cost path using the slope and avoid steep areas (or steep fall line trails), as far as I understood it. That's what I did for now.

What I need is a trail, which is either not steeper than 10 %, independent from the slope, or whose trail grade is not more than half of the slope.

I try to set up a method for a bike trail suitability analysis based on multiple indicators. These two criteria are conditions for sustainable trails regarding erosion and water runoff. The trail would have a start and end point or several possible start and end points.

If I was not clear: Trail grade is the steepness of the trail, slope the steepness of the hill.

I'd also be glad with a corridor instead of one specific narrow path.

Further, I'd prefer a QGIS solution, but could also work with ArcGIS.

• @BERA I've just edited my question! – Kevkev770 Dec 12 '17 at 10:24
• A slope raster should be enough? For example with green colors <=10 % slope and red >10%. The green would be your corridor – BERA Dec 12 '17 at 10:42
• @BERA but then I still only have the slope from DEM which might be a good start. But how could I calculate trail grade then? (It might still be possible to build a trail with 8% grade in the green area, where I'd prefer trail grade to be max. 1/2 of slope) – Kevkev770 Dec 12 '17 at 11:03
• @nagib this looks interesting! did you find a QGIS solution for PEGGER in the meantime? – Kevkev770 Dec 12 '17 at 11:08