Data limitations – Disaster management

Cross border vs internal mobility 

Mobile network operators’ (MNOs) operations are limited to individual countries. This has particular implications for understanding the displacement of people by a crisis as indicators derived from CDR data usually only capture internal movements. As a result, while it may be possible to approximate the range for the number of people displaced from an affected area (assuming no disruptions to the network and representation and that measurement biases are adjusted for), it is only possible to describe the flows of displaced people who remain in the country and not those who are externally displaced.

Damages and network disruptions linked to the disaster

Damage to the country's infrastructure, such as cell towers and outages, can impact the analysis of CDR data. Damage to the mobile network infrastructure may cause outages in some areas, especially the areas which have been most impacted, resulting in an absence of mobility observations within the most affected areas for the duration of the outage which may last up to a few days. 

Additionally, increased call volume ‘saturating’ a cell tower - or damage to a cell tower - may result in network events in its locality being routed by a cell tower in another location, giving the impression of movement to a new location. Research is currently underway to find ways to eliminate these 'teleportation' issues by filtering out apparent flows of which speed is too high to be plausible.

Changes in mobile phone usage

A crisis may result in a change in the use of mobile devices. People seeking and sharing information may increase their use of their mobile devices while network outages or the lack of access to electricity to recharge devices may cause network activity to decrease. During Cyclone Mahasen in 2013, for example, mobile device usage increased sharply in Bangladesh with as much as a 10-fold increase in some heavily affected districts. This change in activity levels may give the impression of a change in mobility where there is none if not accounted for.