A closer link between the city and food production, which has been largely lost since the mid-20th century, would be an essential basis for more sustainable cities. The majority of all cities offer little ground-level open space for growing vegetables, for example. However, the use of rooftops and derelict buildings - commonly referred to as ZFarming (Zero Acreage Farming) - can make notable contributions to inner-city self-sufficiency.

The potential for this is great, as the article by Susanne Thomaier, Axel Dierich and other authors points out, but so far it has hardly been exploited. Using a number of pioneering projects around the world as examples, the scientists illustrate the many additional benefits of rooftop greenhouses, intensive greening and indoor farms: ZFarming enables food production with highly efficient resource recycling as well as several other positive side effects in an ecological and social sense.