The global spread of mobile devices provides new opportunities for better understanding human population mobility, density and characteristics, and for addressing current data gaps.

The International Telecommunication Union (ITU) estimates that:

  • 97%

    of the global population have mobile network coverage

  • 90%

    of those are in the least developed countries (LDCs)

  • 110

    Number of mobile-cellular telephone subscriptions per 100 people

  • 76

    Number of subscriptions per 100 people in LDCs

Call Detail Records (CDRs) are a type of information routinely recorded by mobile network operators (MNOs), a provider of wireless communications services, about the use of the network by subscribers.

Each time a subscriber is involved in a network event - whether that is making or receiving a call, sending or receiving an SMS message or using mobile data - the MNO records information including an identifier of the subscriber, what time of network event it was, when the event occurred and the cell tower it was routed through.

MNOs use this information for billing purposes. However, the combination of an ID for the subscriber, the time of network event, and the location of the cell tower that routed it can also be used to map the approximate locations of the subscriber at given times.

Indian man on phone - landscape. Photo credit: Annie Spratt, Unsplash
Muhammadtaha Ibrahim Hfc8muqulj8 Unsplash

By linking together the locations of a subscriber over time, we can retrieve individual trajectories potentially showing a record of an individual’s movements.

By combining, or aggregating, the trajectory data for many subscribers, we can study patterns in movement of the population as a whole and produce insights which can be useful in a broad range of areas.

Grouping a sufficiently large number of subscribers derived from CDR data together (this process is called ‘aggregation’) also protects the individual privacy of mobile phone subscribers by preventing the movements of any single subscriber from being discernible.

In this section, we will introduce you to the fundamentals of CDR data: