Movement into urban areas is occurring on a staggering scale, over 70 million people a year. The world is now 53% urbanized, compared to 29% in 1950 and 39% in 1980. By 2050, some 70% of the 9.6 billion humans will live in cities, and we could have as many 100 “megacities” (population over 10 million), against 24 such cities today.