If you plan to run an extended adventure -- or even a whole campaign -- in an urban environment, it's important to put some time and effort into describing the details of your city. Chapter 5 of the Dungeon Master's Guide for D&D v.3.5 provides a basic framework for describing some key features of a city, such as its power centers, assets, and highest-level nonplayer characters. This web enhancement expands that basic system into one that is more complex, but well worth the extra work in terms of the payoff for running a city-based campaign.