Hmm, I use Inkscape for making pretty graphics, but I've never used GIS.

I think Hai-Etlik may know more about this, as I understand this is his field and I know he uses Inkscape, but he isn't always around. I did, however, search through his threads and found this one: Some pointers for using GIS. It's not really about Inkscape though, more about QGIS. Not sure if that's helpful or not. Also, Francissimo did a tutorial too, though, again, it wasn't with Inkscape. Not sure if these guides are really what you're looking for. I can't recall seeing a GIS/Inkscape tutorial, though there could well be one lurking in the dusty archives somewhere. Sorry I can't be more help.