figure 1. Median daily range of cellphone users living in central La, sf, and Ny (darker
the radii of the inner, middle, and outer circles represent the 25th, 50th, and 75th percentiles of these
ranges across all users in that area. all maps are drawn to the same scale.
CDRs are an attractive source of
location information for three main
reasons: They are collected for all active cellular phones, numbering in
the hundreds of millions in the U.S.
and billions worldwide; they are already being collected to help operate
the networks, so additional uses incur
little marginal cost; and they are continuously collected as each voice call
and text message completes, enabling
At the same time, CDRs have two
significant limitations: They are sparse
in time because they are generated
only when a phone engages in a voice
call or text-message exchange; and they
are coarse in space because they record
location only at the granularity of a cellular antenna. Not obvious a priori is
whether CDRs provide enough information to characterize human mobility in a useful way.
Since 2009, we have pursued a research program aimed at developing
sound analysis techniques for exploring aspects of human mobility using
CDRs and shown that CDRs are indeed
useful for accurately characterizing important aspects of human mobility. Our
results to date include the following:
Daily travel. We have determined
how far anonymous populations of
hundreds of thousands of people travel
every day in the Los Angeles, San Francisco, and New York metropolitan areas;
Carbon emissions. We have calculated the carbon emissions due to the
home-to-work commutes of these populations, accounting for differences in
distance and modes of travel;
Number of workers and event goers.
We have identified which residential
areas contribute what relative number
of workers and holiday parade attendees at a suburban city—Morristown,
Traffic volumes. We have estimated
relative traffic volumes on the main
commuting routes into Morristown.
We validated our results by comparing them against ground truth provided by volunteers and against independent sources (such as the U.S. Census
Bureau). Throughout our work, we
have taken measures to preserve individual privacy. The rest of this article
covers the methodologies and findings
of our human-mobility studies based
on cellular network data.