Most any CAD package provides a "perpendicular to" modifier when drawing entities. Campaign Cartographer 3 from ProFantasy ( http://www.profantasy.com/products/cc3.asp ) is based on such an engine. They have a demo available. I really recommend investing a couple of hours in doing the tutorials before arriving at a judgement of the software, however. Its basic principle of action-object is somewhat different from the currently-popular object-action principle found in most desktop software.