Tracking Human Mobility

By: Peter Thompson


A recent study shows that individuals can be identified through their mobile phone location with only basic use (i.e. non-Smartphone basic use). By tracking human mobility, researchers have shown that with only four spatial-temporal points, mobile phone datasets can be combined with publicly available information to easily identify an individual.


Each time a phone accesses a network, it must send a signal to a carrier. For example, a phone may contact a network tower to send and receive calls or texts. The signal is picked up and serviced by the strongest carrier, typically the closest carrier, thereby enabling one to determine a spatial point for the origin of the signal. Whatever carrier is accessed must service or store the signal received, and thus create a log of the signal, which is time-stamped and provides a temporal data point. Using just four of these spatial-temporal points, randomly chosen, was enough to uniquely identify 95% of the 1.5 million person sample size. Of course, typical smart-phone use — e.g. push notification for email, location sharing, etc — create many more data-points, thereby increasing the uniqueness and identification capability of each mobility trace.


When these mobility traces are combined with publicly available data, such as home or work addresses, it is not difficult to identify the owner of each trace. Such identification can be used to determine potentially sensitive information about an individual; for example, religion based on churches attended, medical issues or addictions based on clinics visited or meetings attended, relationships based on location pairing, etc. The study offers no conclusion about the effects that human mobility tracing will have on privacy policy, but it acknowledges that mobility data must be taken into account in developing such policy going forward.