A vertical farm is an urban agriculture concept whereby food is grown in and on top of buildings in city areas. In order for this process to work, urban farmers use a variety of techniques, including hydroponics -- cultivating plants in water -- and aquaponics, which uses by-products from fish farming to assist hydroponic growth.

http://edition.cnn.com/2012/05/29/us/plant-chicago-eco-farm/index.html