Slope Ratio Calculation

Hello All, I’m new around here and to grasshopper. I would appreciate if any guru can guide me with a formula. I have topographic surface and would love to have areas of the topo that are %20 slope and smaller. Attached is the surface. Please share a formula if uou could
XXXXXXX.3dm (623.1 KB)

Hello
did you consider searching on internet or this forum ? By default discourse shows under this discussion related topics

If you want to use a plugin (Nautilus) and transform your surface to a mesh.

slope = tan(angle(normal , Z)) * 100

Some curves, without plugin but points on border are not good !


slope analysis no plugin.gh (368.1 KB)

Dear Laurent - that fantastic what you did.
Appreciated alot
cheers