By 2050, two-thirds of the world's population will live in cities. That means already overcrowded cities will have to squeeze in an extra 2.7 billion people. For many cities in the developing world, that will mean sprawling to three times their current size.
To help cities better plan for the future, researchers at the Lincoln Institute of Land Policy and the NYU Stern Urbanization Project took a look at exactly how much cities have sprawled so far. Their Atlas of Urban Expansion maps out the recent growth of 120 cities. In a series of mesmerizing videos, the team mapped the growth of 30 of those cities in detail.
"What we've been able to show is that there's been unbelievable expansion," says Shlomo "Solly" Angel, a senior researcher at the NYU Stern Urbanization Project. "This gives planners and policymakers an idea of by how much cities are going to grow. In sub-Saharan Africa, for example, cities are going to grow seven or eight times between now and 2040."
The idea for the atlas came after meeting with mayors who literally didn't believe projections of future growth. "They'd estimate growth of 25%, and I'd say, no, your city is going to double or even triple," Angel says. "They'd laugh me out of the room. Then I realized I had to stop talking to mayors and start collecting data on urban expansion."
In the past, similar projects had only looked at one city at a time. "We had to do it in a convincing way," Angel says. "If it's a city here, a city there, you learn nothing." The team looked at every large city in the world—a list of 4,000—and then narrowed that down to a sample of 120 cities.
The project also focuses on sprawl instead of population. "Cities grow in population, but nobody can do anything about that," says Angel. "But if you translate that to land, you can do something. You can say, look, we need double the amount of land to accommodate the people."
The research team will come out with a new version of the atlas next year with 200 cities. And they're also working directly with some cities, including Ethiopia, India, and Ecuador, to help them plan.
By understanding the data, Angel explains, cities can reserve just enough land for much-needed public infrastructure and parks, and prepare for housing booms. Ultimately, that planning can lead to cities that are more equitable, sustainable, and livable, instead of sprawling slums.