I read something somewhere, that you can set the terrain editor to minimum and maximum, and that on the minimum setting, the cursor will only draw on areas that are lighter than the color you're using to draw with. So you don't slop over into the black areas. Something like that anyway. If I could remember the URL I'd send it to you. This guy had built a tractor all out of lattices and terrains and it was extremely detailed and he showed all his techniques. It kicked ass

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