Cities with a large amounts of vacant housing are shown on the map. [Photo from web]

Baidu.com, as the most popular search engine in China, can use location data of online users and recorded residential area data to learn if a large number of houses are vacant in a city, cnbeta.com reported on Thursday.

The data Baidu collects includes users' ID, longitude and latitude and the time, which was collected from 9:00 am to 6:00 pm everyday from Sept 8, 2014 to April 22.

The researchers then use an algorithm called "DBSCAN" to calculate the residential density of an area.

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