In the case of an outdoor map like that I'd say you're better off doing it outside maptool and importing it. Maptool doesn't do soft edges well when you're drawing textures so it's hard to have a smooth edge from a road to an angled bluff. Now importing it from an outside program you can do that just fine. Make sure that you set the scale correctly when you're drawing it - probably 50 pixels per grid cell in this case - so that the grid will line up properly when you drop it into maptool.