Here is a think-out-of-the-box article about the “vertical farm”.
It is an interesting vision of a replacement of agricultural land, by indoor robot-tended hydroponic agriculture. They also envision the possibility of raising farm animals and developing aquaculture in the water used to grow the plants; and the fish waste would be used as fertilizer.
All of this would be grown in a 30-floor skyscraper located in the city, powered by the energy coming from city sewage, and the ground floor would be a food supermarket that would provide food for 50,000 people.
Such projects are under review in Abu Dhabi, South Korea, Seattle, WA and Las Vegas, NV.
It looks like science-fiction, yet there are some really interesting arguments in favor of such a development.