This is Wahroonga Farm's attempt to demystify the world of GPS.
Copied by permission from GPS Australia Forums
Wahroonga Farm wrote:
City and town map details are derived from high resolution 'up to date' maps. Many other sources are employed to ensure relevant map data. As you move into the country areas the resolution of the map source generally decreases.
So perhaps a few more images comparing 25k 'raster data' to Garmin City Navigator 2008 'vector data'.
The two maps show images of Gloucester, NSW
Mapsource view 500m zoom
Ozi view at an equivalent zoom. It's a pretty handy map. Notice additional tracks and information showing on the raster map.
It is my understanding (could well be wrong) that Garmin and Oztopo are derived from 100k map day in country areas.
Anyhow, that's my rough take on GPS maps. I hope it's helpful. 
