"OpenStreetMap (OSM) is a collaborative project to create a free editable map of the world.
"The maps are created using data from portable GPS devices, aerial photography, other free sources or simply from local knowledge. Both rendered images and the vector graphics are available for download under a Creative Commons Attribution-ShareAlike 2.0 license".
"OpenStreetMap was inspired by sites such as Wikipedia; the map display features a prominent 'Edit' tab and a full revision history is maintained. Registered users can upload GPS track logs and edit the vector data using the given editing tools" .