How smartphones are solving one of China’s biggest mysteries

For decades, China has been engaged in a building boom of a scale that is hard to wrap your mind around. In the last three decades, 260 million people have moved from the countryside to Chinese cities -- equivalent to around 80 percent of the population of the US. To make room for all of those people, the size of China's built-up urban areas nearly quintupled between 1984 and 2010. Much of that development has benefited people's lives, but some has not. In a breathless rush to boost growth and development, some urban areas have built vast, unused real estate projects -- China's infamous "ghost cities." These eerie, shining developments are complete except for one thing: people to live in them.

New research from Baidu, one of China's biggest technology companies, provides one of the first systematic looks at Chinese ghost cities. Researchers from Baidu’s Big Data Lab and Peking University in Beijing used the kind of location data gathered by mobile phones and GPS receivers to track how people moved in and out suspected ghost cities, in real time and on a national scale, over a period of six months.