CUPERTINO  (AP) — Apple has bought WiFiSLAM, a startup that has been developing a way to use WiFi hotspots to help smartphones navigate large indoor spaces, like stores, airports and conference centers.

The purchase is part of Apple's efforts to bolster its own mapping and location capabilities, after breaking up with Google Inc. last year.

The purchase was reported over the weekend by The Wall Street Journal, which said Apple Inc. paid $20 million for the Silicon Valley company. Apple confirmed the purchase Monday but did not say how much it paid or why it wanted WiFiSLAM.

WiFiSLAM has shut down its website and closed its YouTube account.

Traditional methods of locating cellphones include GPS and sensing of nearby cell towers. Neither of these approaches work well indoors. Retail chains are interested in helping shoppers find things in their stores, and apps that could help them navigate the aisles could be valuable. ABI Research estimates that the market for "indoor retail location" aids will be worth $5 billion in 2018.

Apple initially relied on Google to supply the default mapping and location application for the iPhone, but launched its own "Maps" app last year. The features of Google's iPhone app had been lagging those in the company's app for its own Android operating system. Among other things, the Android app included indoor navigation for some malls and airports.