Hi Gary, > so > r.mapcalc "result=if( isnull(Bones_AVE),0,outputmap)" > > Is that right, no need for A=Bones_AVE? > could the output map be the original? Or does it have to be a new raster? r.mapcalc "result=if( isnull(Bones_AVE),0,Bones_AVE)" and yes, it can be the original r.mapcalc "Bones_AVE=if( isnull(Bones_AVE),0,Bones_AVE)" Achim