i am curious about the different between proprietary map (paid map on sale in Garmin website for example) and free maps (which can be dl from mapping interests groups like gpsfile depot and openstreetmap).
Understand that proprietary map receives their mapping data from from national mapping agencies like U.S. Geological Survey and Ordnance Survey. Where does open source / free maps receive their mapping data from?
The bulk of the data in OSM is collected by volunteers They go out, record tracks with GPS devices, make notes.
They then use editors (software) to add the data to a central database. They can use aerial imagery (e.g. Bing, never Google) to trace features as well.
There are data imports in OSM as well (e.g. all addresses and buildings in the Netherlands). However, this can only be done with open data with a compatible license. Those open data sets are typically provided by governments.
Note that some of the Garmin maps are using OSM data as well in some regions or for some specific devices.
Nowadays a lot (probably too much, as you can only be really sure if you visit the place yourself) is done from government mapping, and donated aerial photography. However, the data entry is still done by volunteers. What esscada described is the situation that made OSM possible in the first place, in the UK, where it started.
I believe that US government surveys have always been in the public domain, as has real NASA imagery. Relatively recently, the UK national mapping agency has released data for low and medium resolution maps with licences that allow their use in OSM.
Various companies have made available some of the aerial imagery they have commissioned so that it can be used in OSM, because they hope to make use of the resulting OSM mapping.