A Quick and Dirty Road Network
Since I didn't find any of this kind (my search-fu with this forum's search function is weak, though), and I think it's helpful for others to just look it up, instead of exploring what the GIMP, PS, and other tools offer, I decided to write it up, prettify it a little, and attach my tutorial as PDF.
It'll take you from
Lack of artistic merit due to utilitarian expediency. That's my story, and I'm sticking to it. ;)