The impact on food resources can be substantial. China supplies almost all its vegetables within its metropolises. City farming can also achieve surprising efficiency. By raising a variety of crops in a confined area with little water, urban agriculturists obtain yields for produce that are several times as high per square meter of cultivated land as those achieved by rural farmers. At the same time, they deliver fresher produce and avoid transport and distribution costs.
Urban agriculture is the antonym of the monoculture.
In Peru, guinea pigs are raised in cages that hang on apartment walls. Farmer cooperatives in Calcutta produce tilapia, carp, rohu and other fish in treated sewage water, supplying one fifth of the fish consumed there. Farmers agree to maintain a tract or a body of water in exchange for the right to grow food on land they do not own. These practices do more than just keep stomachs full. According to the UNDP report, women in a cooperative in Bogota, Colombia, that produces several dozen varieties of hydroponic vegetables earn three times more than their husbands do.