From the PDF Introduction
A Web Enhancement for the Dungeon Master's Guide (D&D 3.5e) v3.5
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.