Crowd-mapping With Cell Phones

Cellular data can reveal where people spend their days

2 min read

Crowd-mapping With Cell Phones
Sources: Ramón Cáceres, James Rowland, Christopher Small, and Simon Urbanek, “Exploring the Use of Urban Greenspace through Cellular Network Activity”; Fabio Manfredini, Paola Pucci, and Paolo Tagliolato, “Deriving Mobility Practices and Patterns from Mobile Phone Data”

To determine the ebb and flow of city dwellers, public officials have typically resorted to looking around and counting. But now censuses can be taken every few milliseconds, as phones ping cellular networks and reveal their location.

For instance, Italian [PDF] and American [PDF] researchers generated usage maps for Milan and the borough of Manhattan in New York City using anonymized cellular data. Paolo Tagliolato, a postdoc at the Polytechnic University of Milan, says such anonymized data are effectively free and always up to date. Conversely, he says, Milan’s last comparable citywide survey was costly, involved 750 000 interviews, and hasn’t been updated since 2002.

09DataFlowMilanFig5Between 10 a.m. and 8 p.m. on Saturdays, shopping and leisure activities in Milan’s city center dominate. Sites like museums on the outskirts also show up.

09OLDataFlowMilanFig4From 8 p.m. to midnight on Saturday, patterns shift, as people congregate in the residential areas that ring the center (background activity has more pink due to a different color scale).

09DataFlowMilanFig2This data, captured between midnight and 8 a.m. during the 2009 Milan Design Week, reveal overnight activity northwest of the city in preparation for daily events.

09OLDataFlowaUsage data captured on a Saturday afternoon in February 2011 show high calling activity from the wealthy residential areas bordering New York City’s Central Park.

09OLDataFlowbA Saturday afternoon the following July reveals a different pattern, with cellphone activity shifting to the southern end of Central Park.

09OLDataFlowcSubtracting the winter map from the summer map reveals the calling pattern more clearly, as wealthier residents leave the city during summer weekends and those who remain flock to the park.

This article originally appeared in print as “Ten Million Censuses Per Day.”

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