Tech talk, cold comfort.

If you want to figure out how many people live in a particular part of your country, you could spend years conducting home visits and mailing out questionnaires. But a new study describes a quicker way. Scientists have figured out how to map populations using cellphone records-an approach that doesn't just reveal who lives where, but also where they go every day.

"This is the first time people have provided statistical evidence that population data produced from cellphone records are of really good quality," says applied mathematician Renaud Lambiotte of the University of Namur in Belgium, who was not involved in the study.