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Since 1988, the population along China’s Pearl River Delta has grown by a whopping 32 million people. Now boasting a total population of 42 million, it’s the largest urban area on the planet. To put it into perspective, 42 million people is more than the population of Canada, Australia, or Argentina.

Just 27 years ago, the medium-sized cities of Shenzhen, Guangzhou, Foshan, and Dongguan were surrounded by mostly rural areas. But as these satellite images show, these cities have grown so rapidly that they’ve merged into a massive, interconnected megapolis.

NASA explains more:

If taken as one entity, the Pearl River Delta region has overtaken Tokyo as the world’s largest urban area—by size and population—according to an analysis of satellite and demographic data published by the World Bank. Between 2000 and 2010, the Pearl River Delta’s urban spaces—defined as areas where the built environment covered more than 50 percent of the landscape in a given pixel—had expanded from 4,500 square kilometers to 7,000 square kilometers. (In 2010, Tokyo had a population of about 32 million people and covered about 5,600 square kilometers.) In the study, researchers used satellite data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) and land cover data from the Landsat program. They also used demographic data prepared by the AsiaPop project.

No other areas in China feature this pattern of growth.

[ NASA Earth Observatory ]

Email the author at and follow him at @dvorsky. Top image by NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey.