File this under “the enemy of my enemy is my friend:” Microsoft is reportedly lending “big support and big dollars” to an open source mapping project in order to counter Google Maps.

OpenStreetMap, which is run by the U.K.-based non-profit OpenStreetMap Foundation, is a self-described “free wiki world map” which operates much like Wikipedia. Volunteers contribute geographic data, which is then free to use for street maps or other purposes.

Computerworld reports that one of the biggest volunteer forces behind OpenStreetMap is none other than Microsoft. It appears the motivation may not be completely altruistic. Not only does support of OpenStreetMap potentially weaken Google’s dominant grip on the market, but it’s reported that Bing also uses OpenStreetMap data for its mapping service.

Some of this relationship should come as little surprise. The founder of OpenStreetMap and chair of its Foundation is Steve Coast, who was hired by Microsoft in late 2010 to work as principal architect for Bing Mobile. Computerworld cites reports, though, that in addition to Coast’s time, Microsoft’s Bing has contributed “valuable map data” to the OpenStreetMap project.

And all that data — plus increased fees for Google Maps — has led several companies to switch. Apple this month began using OpenStreetMap for its iPhoto app on the iPad and iPhone.

A quick scan of OpenStreetMap Foundation site doesn’t show Microsoft listed as a direct financial donor. But its non-cash contributions appear to be paying off for Bing and other project data users.

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