Mapping a New, Mobile Internet

Imagine that your business had a complete log of your customers' wanderings—every trip to the grocery store, every work commute, every walk with the dog. What could you learn about them? Armed with that knowledge, what sorts of goods and services might you try to sell them? Just as important, if you made your best pitch—relevant and timely, of course—would customers concerned about privacy tell you to get lost? This isn't science fiction. A nascent industry extending from the laboratories of Google (GOOG) and Nokia (NOK) to a host of data-fueled startups is wrestling with these very questions.

On a snowy winter evening in New York's SoHo neighborhood, a small team of analysts at a startup called Sense Networks is poring over the movements of nearly 4 million cell-phone users over the course of a year. They have been tracked by global positioning systems, by cell towers that catch their signals, or by local Wi-Fi networks that detect their presence. As far as the Sense analysts can see, these people have no names: They are simply dots moving across the maps on Sense's computers. (The data trove comes from a company New York-based Sense will not name.)