Nicely, Done, Mini! I like the subdued "feel" of the map, with muted yet noticeable textures. Your color scheme is also well chosen. I'm not sure what the lines with 120' next to them are, though; bridges?
GIMP is a great program, Jaerdaph; I used it many times myself before Photoshop, and I never felt overly limited. There are lots of tutorials & helps on the 'net too.
Again, nice work, Mini!