Satellites and drones can capture outstanding surveys of infrastructure, but for tracking people after a disaster, phone data is becoming indispensable. Flowminder, a Swedish not-for-profit organization, demonstrated that anonymized call records from mobile phone operators could be used to map flows of displaced people following the 2010 earthquake in Haiti, and updated its model immediately before the 2015 Nepal earthquake.

Following that disaster, Flowminder used anonymized data from 12 million phones to estimate population displacement, including gender and age distributions, down to 100m resolution. Following the disaster, each day the Nepalese mobile provider Ncell delivered a 12-gigabyte CSV file to Flowminder, which reformed the data, assigned call locations to administrative regions, and interpreted migration patterns.

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