From Introduction:
Urban Decay is a collection of source material for the Metropolis Rho campaign setting as described in the adventure [Humanity In A Bottle], which depicts a degenerating society in the far future, more than two hundred years after the nuclear holocaust known as “the Fall”. Isolated from the desolate world outside by its own ancient city dome, Metropolis Rho presents an ideal Degenerate community for GMs to base new campaigns in.
The material herein is intended to serve as background information for both GM and players alike, giving a history of the city, an overview of its culture and inhabitants, class divisions, and a glimpse of the elements that make it an iconic Degenerate community. In addition to “setting the stage”, Urban Decay presents guidelines for making characters from the city, including suggestions on how standard Darwin’s World occupations and even variant backgrounds can be incorporated into the setting. A number of new weapons and items are also introduced here, as well as three new advanced classes that make an appearance in the Humanity In A Bottle adventure.