This is the most efficient way of producing food. Market Gardens on Unused Land beside railway lines, in hospital grounds. One study of 86 American cities found that there was almost enough idle land in those cities to feed all the people in them. Edible Landscape Roadsides, parks, school grounds, planted with fruit and nut trees to provide free food and materials. All Flat Rooftops can be gardened.
City centres have vast areas of unused space.
Convert most land to useful purposes. Lawns take enormous amounts of water, fertilizer and energy. Dig up most roads , eventually, and use the space for gardens etc., including space taken by parking lots, garages, and petrol stations. Facilitate movement of many people from cities to country towns making more space in cities for gardens. There would also be many varieties of animals living in our suburbs, including an entire fishing industry, based on tanks and ponds.