Oh, one thing I've learned from Jürgen Hubert, who has created a world all about cities, is that having a strong visual theme is also a good idea. In Jürgen's case, the cities in his campaign setting are all based around a common visual theme, the Nexus Tower - these massive magical towers at the hearts of cities and metropolises that draw upon the very life force of those near them.

Personally, from a roleplaying perspective, I think it is a good idea to have a central feature for key cities or locales that acts as a verbal cue to the players, something that they are always reminded of by the GM whenever they visit. In most cases, it might be visual in nature - a fantastic tower, a tremendous bridge, or the like. In other cases it might appeal to some other sense - a certain smell, the dampness of endless fog, or even a sense of foreboding.

While my earlier post addressed the verisimilitude of a city, GMs shouldn't forget the amazing cityscapes side of fantasy, if they have the opportunity for it.