Not likely I'm afraid. The best plan would be to create (or get hold of) a set of objects such as trees and buildings and then paste them into place to build up the map. As the outdoor environment is so much less constrained than the indoor maps it relies quite a lot on freehand drawing. Thanks for the compliment on the indoor maps - much appreciated.
Nice tutorial for creating an old-school map in Gimp. Is there any chance you'd be willing to do a tutorial on creating an old-school overland map in Gimp?