Last year, the UN announced that more than half of the world’s population now lives in cities. This followed on from the news that more than a billion people live in slums. As the exodus from rural to urban areas continues, cities around the world are struggling to cope. In this special issue of Geographical, we go inside Mexico City, the world’s second-largest city, with a population of more than 19 million, to see what lessons we can learn from its transition from urban disaster to prosperous global metropolis.

To set the scene, photographer Sophie Gerrard captures the city’s character in a series of candid images