Introduction What Is CDR?
CDR is anonymized digital records collected by MNOs each time a subscriber makes a call or sends a short message service (SMS) through their mobile phone. Subscriber identity module (SIM) numbers and cell tower locations constitute the essential components of CDR data for our purposes; in that respect, CDR data is considered metadata.a,3 When this metadata is aggregated across a large number of people over a significant period of time, it contains many data points and becomes a form of big data. When subscribers use cellular data to access the internet, this also creates records which are stored by MNOs. Although this data could be included in data ba data.
Metadata is a set of data that describes and gives information about other
Disaster event
sharing agreements and analyzed alongside call and SMS data, it is not the focus of this report. Figure 1 below shows the process of how CDR data captures mobility. CDR has been used in multiple contexts in recent years, including to aid in humanitarian disasters, since 2010.b For example: • Flowminder, a nonprofit that uses mobile operator, geospatial, and survey data to analyze movements of people affected by humanitarian disasters, has used CDR data from the MNO cb A list of projects using CDR and other mobile phone technologies to inform migration policy and research can be found in the “Data Innovation Directory” from the Migration Data Portal. https://migrationdataportal.org/data-innovation
Figure 1: How CDR captures human movement
Network
Sender
When a disaster such as a hurricane hits, the user sends or receives a call or an SMS with their mobile phone, which contans a SIM card.
Cell tower 1
The SIM card “pings” the cell tower nearest to the sender, in order to connect with the mobile phone network to which the SIM is subscribed.
MNOs collect CDR data in order to bill their customers; SIMs are matched to subscribers’ names during the billing process. For developing a general understanding of the caseload or flow of displacement after a disaster, or of human movement to inform a public health response, humanitarian actors and stakeholders considering the use of CDR do not require all the components of MNOs’ customer activity data.
Cell tower 2
The network transmits the call across towers until it reaches the tower nearest to the intended receiver, at which point the tower connects to the receiver’s SIM.
Receiver
The location data for both starting and ending towers is recorded, and the event is timestamped (in red).
CDR data that has been 1) anonymized, 2) aggregated, and is less specific in either the 3) timing or 4) geolocation of the call can prevent the identification of individuals through personal data. Because it is critical to ensure that individuals’ identities are not compromised in humanitarian settings, this report focuses on applications of aggregate and anonymized CDR data; unless otherwise specified, all references to CDR data in this report assume the data is in this form.
Introduction
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