That's pretty cool, if only it could be done in GIMP. Has any one noticed how off topic we've gone?
I'm sure it's alright, as long as we are providing helpful insight, rather then steering this topic towards the wasteland sewers.
Anyways, it may be able to work on GIMP. I can't guarantee. If anything, the fonts would give you grief. If you really need a map like this, I can help you out sometime. You could draw out general shapes on paint or something and send that me, and I'll do the fancy stuff with the shapes on photoshop, using her maker. Only takes a few minutes.
And the word placements, trees, mountains, etc, can all be done on GIMP, I believe, so you could customize it. I wouldn't say I'm all too good at it, though. The edges look a little too repetitive when I do it, I think D: