Faced with the incomprehensible scale of worldwide mega-urbanization, observers have alternately fallen back on sheer numbers or city comparisons to drive home the speed at which cities in the developing world are growing. For example, New York University’s Shlomo "Solly" Angel projects the world’s urban population will double in 40 years, while urban land cover—including everything from skyscrapers to slums—will triple in size during that span. Grasping to put such numbers into context, the McKinsey Global Institute estimates China will build the equivalent of New York every other year for 20 years, while India needs to add the equivalent of a Chicago to its building stock annually.
The mind reels, but such comparisons tell us little about the truth on the ground—is the urban future of India more likely to look like Chicago or Dharavi (Mumbai’s famous slum) or something else completely? A satellite designed to measure ocean winds offers us a clue.
University of New Hampshire Earth system scientist Steve Frolking, together with researchers at Yale and Boston University, recently published a paper plotting the growth trajectories of a hundred cities over a decade, combining satellite data on the spread of city lights with recordings from the SeaWinds scatterometer mounted on NASA’s QuikSCAT planet observation satellite, which operated from 1999 until 2009. Typically used to measure the effects of wind on the oceans’ surface, the sensor’s microwave transmitter also bounced signals off the cities in its 1,800 kilometer-wide orbital path.
Frolking broke each city down into a grid, plotting each cell as an arrow with its trajectory rendered over time: the head corresponds to 2009, the tail to 1999. In doing so, we can see how each section of the city, from the exurbs to the CBD, changed over the decade in question. The longer the arrows extend horizontally means that the part of the city has expanded outward. The longer they extend vertically shows that the city is expanding upward, building more towers. The results tell three distinct stories about humanity’s recent urban evolution.
The first is that Indian cities—joined by many in Africa and Latin America—have sprawled out rather than up. Whether Bangalore, Hyderabad, Delhi, Kolkata, or Pune, the fastest growth occurred at the cities’ edges, while the core remains low-slung.
At the opposite end of the spectrum, Frolking and company found that developed world capitals such as London, New York, and Tokyo added considerable mass and height to their skylines while growing slowly, if at all on the periphery.
And to no one’s surprise, China’s megacities did both. Not just Beijing and Shanghai, but also second-tier cities such as Shenzhen, Dongguan, Foshan, and Tianjin experienced patterns of growth that resemble no other nation on the planet—a point that paper co-author Karen Seto, who has studied Chinese urbanization for decades, drove home in her presentation at a "science of cities" confab at Arizona State University last month.
"I had never studied cities before, and what struck me was the fundamental difference in backscatter between China and India, where the population sizes are similar, but the pattern is totally different," says Frolking. Because the SeaWind went offline in 2009 when its antenna failed, more recent data isn’t available, but Frolking is hopeful that a new Indian satellite may yield higher-resolution results. "This is still a really blurry view of the planet."