In 1800, less than 2 percent of the world’s population lived in cities; by 1900 the share was still only about 5 percent. By 1950 it had reached 30 percent, and 2007 became the first year when more than half of humanity lived in cities. By 2016, the United Nations’ comprehensive survey found 512 cities with a population greater than 1 million, with 45 of them larger than 5 million and 31 surpassing 10 million. This largest group has a special name: “megacities.”
