Business and finance
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.
Mr Angel and his team pulled this off by developing clever methods to analyse detailed satellite images. In other words, the researchers had computers count pixels to calculate such things as the fragmentation of big cities (meaning those with a population of more than 100,000, of which there were about 4,000 worldwide in 2010, see map). To see how these cities have changed over time, the researchers picked 120 of them and looked at two sets of satellite images, one from 1990 and the other from 2000. And for a representative subset of 30 cities they made comparisons going back to 1800 by digitising and resizing old maps.
Some of the results are predictable. Both urban population and urban land cover have grown between 1990 and 2000 (by 1.6% and 3.66% respectively in the global sample of 120 cities). Most big cities are now “polycentric”, meaning they no longer have a single central business district. And despite the rapid growth of cities in the 20th century (sixfold in the representative sample of 30 cities), the world’s total urban land cover is still small: less than half of one percent of all land area in 2010.
But other results are surprising, in particular those which suggest the existence of “urban laws” that appear to apply worldwide. 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.
Using such results (and the UN’s population forecasts) Mr Angel is able to predict by how much the world’s urban land cover will grow in the decades to come. Assuming conservatively that the urban population densities decline by 1% per year (the real number since 1900 was around 1.5%), the land covered by cities will treble to 1.34% of the global land area by 2050. Yet this low average is somewhat deceptive: 29 countries will see more than 10% of their land covered by cities, including Britain, Italy and Lebanon. And in developing countries, where most urbanisation will take place and population densities are likely to decline most quickly, urban land cover may grow more than six-fold.
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. Seoul, which established a protected greenbelt in 1971, is a case in point. By 1990, the average household in South Korea’s capital had to pay ten times its entire income to purchase a basic housing unit.
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.
Cities in developing countries must be equally ambitious if they want to be able to control the masses of people coming their way, says Mr Angel. They should plan for an arterial grid with roads no more than one kilometre apart and that covers an area big enough to accommodate newcomers for the next 20 to 30 years. And instead of surrounding the city with a greenbelt, they should protect sufficient open space within the city limits.
Committed environmentalists and other defenders of urban containment are sure to reject at what Mr Angel calls “the making room paradigm”. But he makes a solid argument that this is a much more realistic way of dealing with urbanisation than building new city walls, particularly in developing countries. “As heroic and justified as it may be,” he writes, “containing the oncoming global urban expansion is much the same as holding back the tide.”
* “Planet of Cities”, by Shlomo Angel, Lincoln Institute of Land Policy, Cambridge, Massachusetts, 2012