Apple has recently bought a Silicon Valley start up called WiFiSLAM — a company with an indoor mapping technology to figure out a smartphone user’s location indoors where satellite GPS navigation signals can be a little vague.

The potential applications of indoor mapping range from retail to entertainment to personal use. But on the same day Apple bought WiFiSLAM, an academic study came out showing it is quite easy to identify someone by tracking their movements digitally. Researchers writing in Scientific Reports studied 15 months of human movements and concluded all they need is four pieces of location data to figure out who most people are. The authors call this “anonymity risk.” Among the implications: When companies gather location data without names and addresses that doesn’t necessarily protect privacy.

Lindsey Turrentine, editor-in-chief of CNET Reviews, joins Marketplace Tech host David Brancaccio, to explain indoor mapping and how businesses plan to use it.