As I am just getting familiar with GPS via my discontinued nuvi 200 with limited capability, it would be good to get some insight into what is happening with GPS software. In the case of Garmin, it appears that newer units provide a user with software options not formerly available. For example, mapsource. I'm guessing there is more and probably revealed in some way to Garmin users via supplemental manuals.

Then there seems to be open (street) side to all this. I get the impression that this is sort of like Linux, or do your own. It may very well be, for example, that one constructs their on GPS maps or even a collection of people build a particular map. Again, I'm guessing.

What books or documents (web or otherwise) reasonably describe the state of all this GPS world?