James--you are excatly the kind of guy this site is made for, because we ALL love discussing maps! Welcome to paradise, my friend!
I do not know much about Inkscape or GIMP (although some Guild members are really amazing users of those programs), but from what I notice about both your map and Inkscape in general, the results often tend to look "cartoony" (or more accurately, "computer-ish") due to the vector-based nature of the program. It's fine if that's waht you're looking for, of course (ex: a GM map), but if you learn to import into GIMP & do some touch-up you can also really up the interest & quality of your maps. That being said, a talented user can make any program do amazing things; I'm just talking in sweeping generalizations.
But hey, for a quick, first-shot at a map, you have nothing but my praise! Way to go! And once again, welcome.
PS: I'm moving this post to the WIP area, since it fits a bit better there.