Dundjinni is ideal for encounter scale maps, but it doesn't do so well as the scale goes up. CD3 can do some amazing work, but it does take some time to learn how to use it, as it is based on CAD software. No matter what software you're using, though, mapping a city can be very time consuming. There have been some recent advancements here in automating it, though, if you do not need to maintain a strict level of detail. I don't remember which threads off the top of my head, but I suspect if you look for threads by Ascension and RobA you might find some good stuff. Ascension works primarily in Photoshop and RobA in Gimp.