Humanity, for the first time, has become an urban species. The number of people living in towns and cities has grown more than fivefold since 1950 and a decade ago overtook those living in the countryside. And this dramatic transformation is continuing to accelerate.
By 2050 urban areas will have gained another two billion people, and two thirds of humanity - overwhelmingly rural throughout its previous history - will live in them. Nearly 90 per cent of this increase will take place in Asia and Africa.