THE COMMON LANDS - Nezahualcóyotl, Mexico Ciudad Neza is a sprawling expanse of three million people that lies on the northeast edge of Mexico City's Federal District (D.F.). Often referred to as the largest slum in the world, Neza is home to one of the state's most impoverished populations, as well as one of the highest crime rates in the entire country. The tierras comulanes (common lands) on the barren edge of the Neza dump are a last resort. Fringe commnities have developed around the landfill -- which is one fifth the size of Manhattan -- and their residents build shelter and earn what money they can by picking, sorting, and recycling the trash around them. A daily average of 12,000 tons of garbage is dumped on the outskirts of Nezahualcóyotl, but lawsuits from environmental agencies are piling up and space is running out. Mexico has begun to focus on the environmental impact of its waste disposal techniques and is turning toward more sustainable methods, but as a result the primary resource for the unsung residents of the common lands is under close scrutiny.