Daniel Victoria wrote: > Multiply the DEM by -1 > > In r.mapcalc do: > dem_inv = dem * -1 Or just negate it: dem_inv = -dem This is more efficient, although I doubt that the difference would be noticeable in practice; I would expect reading and writing the data to dwarf the computation. -- Glynn Clements <glynn at gclements.plus.com>