Users who download the OpenStreetMap app (and Microsoft Silverlight) can switch between the traditional layers, which include bird's eye, aerial and standard street map views, and Mapnik, a colorful map that includes businesses and landmarks labeled by users and devices through Open Street Map.
Open Street Map crowdsources location data by making it possible for users to add to its database. It's been described as "what would result if Wikipedia and Google Maps made a baby." The project started in the U.K. and grew out of the need for a free location dataset that programmers - and anyone - could use without being limited by, for example, Google's API or Terms of Service.
Open Street Map has been praised for being more detailed than maps compiled by big companies like Google and Microsoft, and its creators hope that with thousands of editors, it will be more accurate. It has more than 250,000 registered contributors and has been steadily growing.
The Bing Maps layer is more detailed in some neighborhoods than others, but you can assume it will only become more informative as users across the world add to it. It's searchable and navigable, just like the other layers. You can't edit or add to the map with the app for Bing Maps - you have to register at Open Street Map.
The announcement of the partnership with Bing comes less than a month after AOL announced a $1 million investment in Open Street Map to fund open source mapping in the U.S. Companies like AOL and Microsoft have an interest in supporting Open Street Map in order to combat Google's dominance in mapping.