[GRASS-user] Slope categories from DEM ?

[Martin Landa]

Hi,

2010/11/6 Emma <emma at seleeg.org>:
> I am new to GRASS and I need to compute, from a DEM, a map showing the areas
> with a slope lower than 30%. So basically I would like 2 slope categories,
> <30% and >30%, but I am quite lost in the way I should do it. Could you
> please sketch me the steps to achieve it?

generate slope map with

r.slope.aspect elevation=dem_map slope=slope_map format=percent

and then reclass slope map by r.mapcalc

r.mapcalc 'slope_30 = if(slope_map > 30, 1, 0)'

r.mapcalc generates raster map with two values - 1 for areas where
slope is greater then 30% and 0 for areas where slope is lower or
equal then 30%.

Martin

-- 
Martin Landa <landa.martin gmail.com> * http://geo.fsv.cvut.cz/~landa