For modern maps, I prefer a vector approach, with Illustrator or Inkscape. Modern life is far less about the terrain that a fantasy or historical map...
300,000 would be an enormous city by Middle Ages European standards. Paris and London, I think, were about that size prior to the plague and reached...
The darkness is easy enough to fix: Just turn down the opacity a bit. I agree with - Max -: at the size you're going to be showing these, the simpler...
It just means that if you use one of those textures, you cannot distribute the resulting map under a Creative Commons (CC) license. You can still do...