A look on how they are trying to use data gleamed from GPS and cell phones to track user behavior.

"We’re in the midst of a boom in devices that show where people are at any point in time. Global positioning systems are among the hottest consumer electronics devices ever, says Clint Wheelock, chief research officer at ABI Research, a technology market follower. And cellphones increasingly come with G.P.S. chips. All of these devices churn out data that says something about how people live."