A urban visualization projects is really challenging for any architectural visualization artist due to the amount of information and objects that might be present on the scene. If your street has lots of threes and vegetation, you will be in serious trouble without a good plan to produce your images. I just saw an interesting project at the Blenderartists forums from an artist called Drabson, where he posts some images of a urban visualization project and along with the renders he posted a link to a making of the project. There you can learn more about the techniques and tricks used to render all images.
