Depending on what you mean by reality mapping, you might find that either Inkscape(free vector based analog to Illustrator) or Illustrator itself to be a better fit vs GIMP/PS. If you don't plan to do much advanced shading or photo realistic mapping, those would likely be a better approach. Things such as street maps, topographical maps, simple line drawings, etc would be more in line with Vector programs. Also, if you plan to do much in way of actual drawing, I would highly suggest investing in at least a low end(Wacom brand would be the only recommendation I would make) tablet. You will find it makes things far easier than a mouse depending on how much "drawing" you plan to do.