GROWTH, unemployment, industrial production—data for comparing countries is in rich supply. But if economists want to analyse and contrast cities, they have less to go on: most information is not standardised and is thus hard to compare. This is a problem, given the world’s rapid urbanisation and cities’ ever growing economic weight: the UN expects the urban population to double between 2010 and 2050, from 2.6 billion to 5.2 billion.
A new book goes some way toward remedying this deficit: “Planet of Cities”, by Shlomo Angel*, a professor of urban planning at New York University. To make “a modest contribution toward a science of the city”, Mr Angel and his colleagues generated a lot of comparable data on things such as urban expansion, population density and open space. (...)
On average, cities of all population sizes are growing at the same rate. Population densities have been in decline for more than a century—and not just in rich countries, where many cities have sprawled. It also seems to be a global norm that half of a city’s footprint is not built up. And the distribution of cities within a given country indeed follows the “law” that George Zipf, an American researcher, discovered in the 1940s: that the largest city is always about twice as big as the second largest, three times as big as the third largest, and so on. (...)
The book, however, is much more than an interesting exercise in urban statistics. Mr Angel does not hide his agenda: he wants to demonstrate that the movement of people into cities cannot be stopped; trying to slow down urbanisation and even stop it will produce all kinds of unpleasant side effects, he argues, not least driving up housing prices—which hurts the poor the most. (...)
Rather than copying such efforts to limit urban expansion, as some environmentalists advocate, rapidly growing cities in developing countries should take a page from New York and Barcelona, says Mr Angel. In the 19th century both cities decided to prepare themselves for rapid growth. In 1811 New York’s city council approved a plan which allowed all of Manhattan to be built up and included the island’s now famous street grid. In 1859 Barcelona followed suit with a similar concept to expand the city nine-fold.