Between now and 2050 the number of people living in cities will grow from 3.9 billion to 6.3 billion. The proportion of urban dwellers will swell from 54% to 67% of the world’s population, according to the UN. In other words, for the next 36 years the world’s cities will expand by the equivalent of six São Paulos every year. This growth will largely occur in developing countries. But most governments there are ignoring the problem, says William Cobbett of the Cities Alliance, an NGO that supports initiatives such as the one launched by New York University to help cities make long-term preparations for their growth. “Whether we want it or not, urbanisation is inevitable,” say specialists. “The real question is: how can we improve its quality?”