Apple has spent some of its money acquiring indoor GPS company WifiSLAM.

The acquisition cost $20 million, according to Wall Street Journal sources.

An Apple spokesman confirmed the deal, telling WSJ: "[Apple] buys smaller technology companies from time to time." Apple's spokesperson declined to comment further, according to the report.

On the WifiSLAM listing on AngelList, described as "Where companies meet investors", under the funding tab the following is now listed: "$20,000,000: Acquired, Mar 24, 2013. Apple."

WifiSLAM's website - www.wifislam.com - is now offline.

The two-year old start-up has developed a technology to detect a smartphone's location in a building using Wi-Fi signals. On the AngelList website WifiSLAM explains that its offering allows a "smartphone to pinpoint its location (and the location of your friends) in real-time to 2.5m accuracy using only ambient WiFi signals that are already present in buildings."

The company adds: "We are building the next generation of location-based mobile apps that, for the first time, engage with users at the scale that personal interaction actually takes place. Applications range from step-by-step indoor navigation, to product-level retail customer engagement, to proximity-based social networking."

WifiSLAM had been offering its software to app developers looking for indoor mapping solutions. The purchase should hep Apple improve its Maps offering.

One of WifiSLAM's co-founders is former Google software engineering intern Joseph Huang. It also has backing from Don Dodge, who worked at both Google and Microsoft, notes The Guardian.

Google already offers indoor mapping, such as the inside of Euston Station in London.

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