Returning the world’s population to the countryside isn’t an option. Dividing up the planet into plots of land on which we could all survive self-sufficiently would create its own natural disasters, not to mention begin highly unlikely to ever happen. If we are to protect what is left of nature, and meet the demand to improve the quality of living for the world’s developing nations, a new form of city living is the only option. The size of a city creates economies of scale for things such as energy generation, recycling, and public transport. It should even be possible for cities to partly feed themselves. Far from begin parasites on the world, cities could hold the key to sustainable living for the world’s booming population-if they are built right.