“OpenStreetMap creates and provides free geographic data such as street maps to anyone who wants them. The project was started because most maps you think of as free actually have legal or technical restrictions on their use, holding back people from using them in creative, productive, or unexpected ways.”
Below we can see a comparison between the relatively empty open street map of Macau and the Google maps version. In order to add to an open street map one most collect original gps information to use as a source for retracing the streets. The existent maps are closed and owned by other entities thus the need to create original source data. This is achieved in some places through mapping parties where data collected from one event is combined together. A visualization of one such party done by Information Society or George Metcalfecan be seen here, http://vimeo.com/8033601.