There are some 1600 humans in the Big Rubble, with 500 in the Real City, 300 in Zebra Fort, and 300 in Mani’s Fort. The remaining 500 are scattered around Zebraside, the Zebra Ruins, and the Main Ruins. This covers about 250 hectares in total (the Big Rubble has some 1500 hectares in total)
Zebra Fort is supplied by New Pavis, as is probably half of the population in the Real City. The various bandit gangs trade for food as well. As a result about 600 people within the Big Rubble are fed from New Pavis.
But almost a 1000 people are supplied by food and livestock from within the Big Rubble! Given that the only decent farmland is atop Mani’s Fort or between the ruins and New Pavis, that’s pretty amazing!
In the Main Ruins there are some 800-2000 (!) little gardens inside the husks of ruined buildings. These are tiny and a typical garden is only 20 meters by 25 meters, small enough to fit within a ruined courtyard, the footprint of a collapsed building, or along a broken wall.
They grow a variety of vegetables (cabbages, leeks, beans), herbs, fruits (figs, grapes), benefiting from unexpectedly high fertility—possibly due to magical influences or rich soil from centuries of decay. Integrated with pigs and chickens, these gardens form a resilient, self-sustaining system.
One thing I finally figured out is that it looks like there are about 14.5 km of walls surround the Big Rubble. Which means the area enclosed by them is substantially bigger than the Servian Walls of Rome (11 km). The Big Rubble is about the same area as Ancient Rome at its height.