The map we use on GarminWorldmaps are based on data from OpenStreetMap. We use this data for rendering and converting our own Garmin compatible GPS maps. OpenStreetMap reates and distributes free geographic data for the world. They started it because most maps are actually not free and have legal or technical restrictions on their use, holding back people from using them in creative, productive, or unexpected ways. OpenStreetMap represents physical features on the ground (e.g., roads or buildings) using tags attached to its basic data structures (its nodes, ways, and relations). Each tag describes a geographic attribute of the feature being shown by that specific node, way or relation. http://www.openstreetmap.org
So how accurate are these maps actually?
OpenStreetMaps are compared to other maps are equal in details and accuracy. Thousand and thousands of people word on this map every single day to improve it.
They show Motorways, Street Names and small Tracks. As well as thousand of POIs (Point of Interest) like Hotel, Filling stations, Supermarkets, Hospitals, and many more. http://wiki.openstreetmap.org OpenStreetMap’s dataset has grown to unprecedented size. The database now contains over 21 million miles of road (33,968,739 km) data and 78 million buildings.
more statustics at http://wiki.openstreetmap.org/wiki/Statistics