Mobile-Phone Mobility Estimation

Mobile-phone mobility estimation uses the digital traces left by ordinary phone use — call detail records, or CDRs — to map where people are, how their numbers shift over time, and how they move between places. Deville and colleagues' 2014 study in PNAS demonstrated that the locations of cell towers handling each call, aggregated across millions of subscribers, can produce dynamic population maps that track seasonal and daily changes far more finely than a decennial census ever could. Because a CDR records which tower served a user and when, the method can infer each person's habitual home location, count how many people 'live' in each area, and detect when those homes shift — the signature of internal migration or displacement. The approach turns a byproduct of telecom billing into a near-real-time demographic sensor, especially valuable where censuses are infrequent and crises move people faster than official statistics can follow. Crucially, the estimates are calibrated and validated against census or survey ground truth, so the phone-derived figures are anchored to known totals rather than taken at face value. The result is a powerful, if ethically fraught, way to observe human mobility at scale.