Remotely measuring populations during a crisis by overlaying two data sources.
BACKGROUND
Societal instability and crises can cause rapid, large-scale movements. These movements are poorly understood and difficult to measure but strongly impact health. Data on these movements are important for planning response efforts. We retrospectively analyzed movement patterns surrounding a 2010 humanitarian crisis caused by internal political conflict in Côte d'Ivoire using two different methods.


METHODS
We used two remote measures, nighttime lights satellite imagery and anonymized mobile phone call detail records, to assess average population sizes as well as dynamic population changes. These data sources detect movements across different spatial and temporal scales.


RESULTS
The two data sources showed strong agreement in average measures of population sizes. Because the spatiotemporal resolution of the data sources differed, we were able to obtain measurements on long- and short-term dynamic elements of populations at different points throughout the crisis.


CONCLUSIONS
Using complementary, remote data sources to measure movement shows promise for future use in humanitarian crises. We conclude with challenges of remotely measuring movement and provide suggestions for future research and methodological developments.
Department of Biology, Center for Infectious Disease Dynamics, Penn State University, University Park, PA 16801, USA nita@psu.edu.
Nita
N
Bharti
College of Information System and Management, National University of Defense Technology, 410073 Changsha, China Flowminder Foundation, 17177, Stockholm, Sweden Department of Public Health Sciences, Karolinska Institutet, 17177, Stockholm, Sweden Division of Infectious Disease, Key Laboratory of Surveillance and Early-warning on Infectious Disease, Chinese Centre for Disease Control and Prevention, Beijing, 102206, China.
Xin
X
Lu
Flowminder Foundation, 17177, Stockholm, Sweden Department of Public Health Sciences, Karolinska Institutet, 17177, Stockholm, Sweden.
Linus
L
Bengtsson
Flowminder Foundation, 17177, Stockholm, Sweden Department of Management and Organization, Stockholm School of Economics, 11383 Stockholm, Sweden.
Erik
E
Wetter
Flowminder Foundation, 17177, Stockholm, Sweden Geography and Environment, University of Southampton, Highfield, Southampton, SO17 1BJ, UK Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA.
Andrew J
AJ
Tatem
D000533:Altruism; D040421:Cell Phone; D003142:Communication; D007560:Cote d'Ivoire; D003625:Data Collection / Q000379:methods; D004630:Emergencies; D006801:Humans; D008027:Light; D011156:Population Density; D012036:Refugees; D058998:Remote Sensing Technology; D063809:Satellite Imagery; D014857:Warfare
Crisis; Mobile phones; Movement; Population density; Satellite imagery