In the past 20 years, the pendulum has started to swing back. San Francisco's Fresh Start Farms employs homeless families raising vegetables for some of the city's finer restaurants, while at the San Francisco County Jail's Garden Project, prisoners grow food for local soup kitchens, graduating when they complete their sentences to an intensive market garden that serves restaurants and farmers' markets. One of the reasons for this efflorescence is the harsh nature of the modern food-delivery system itself. In this situation, urban agriculture fills the niche abandoned by the corporate food giants. The amount is really a pittance, but it's a start.
Urban agriculture faces many impediments.
Planning departments tend to be suspicious, neighbors don't like the smell of manure, and vacant lots have to be thoroughly tested for toxic substances. City farmers outside the United States have a much easier time of it, and the field is flourishing. Hong Kong, for example, the most densely populated city in the world, produces two-thirds of its own poultry and nearly half its vegetables. In Brazil, slum dwellers raise iguana and guinea pigs to supplement protein-poor diets. Urban farmers in the United States do enjoy some advantages over their country cousins.