try looking here... http://www.cartographersguild.com/showthread.php?9606 its the city I'm working on - first I sketched it (but you don't have to do that), then I started drawing the roads in illustrator - but you can do those in photoshop as well (own layer - everything on its own layer) - now I'm adding building (in form of squares) to the file, afterwards I'll be adding bevels and textures to the elements and finishing touches - all in photoshop. Hope that helps a little