Ah, le weekend… (Image: Leroy Francis/Getty)

Paris empties on a public holiday as citizens flood to the seaside.

Now, for the first time, it is possible to watch a whole country hit the beach using cellphone location data on hundreds of millions of phone calls from 20 million people. The research could also help map places where data on population movement is sparse.

Cellphone data from 2007 shows how the population density of coastal towns like Biarritz and Bayonne shoots up by 50 or 60 per cent on public holidays.


Video: Cellphone use tracks holiday population shifts

On normal weeks, France pulses like a beating heart, its people clustering into Paris from Monday to Friday, before heading out into the countryside on weekends. The study, by Pierre Deville of the Catholic University of Louvain (UCL) and Catherine Linard of the Free University of Brussels (ULB), also covers Portugal.

In developed countries, accurate, up-to-date data on population movement across the nation could help public transport agencies plan services, or help event planners manage large crowds that flock to concerts. Understanding such movement in countries like Sierra Leone, for instance, would let epidemiologists halt the spread of disease, or get help to where it is needed in disasters.

Deville says one of the hardest parts of doing this country-level measurement is getting the data in the first place. His and Linard’s data came from phone carrier Orange, carefully prepared in aggregate to make it impossible to breach any individual’s privacy. One of the main points of the paper is to show carriers that scientists can use their data responsibly, and to highlight the potential value of crunching mobility data on this scale.

The team showed that their results compared favourably with existing studies on human mobility in France, demonstrating that their approach can work for a whole country.

Journal reference: PNAS, DOI: 10.1073/pnas.1408439111