This is interesting...
Just been on a 5Km walk around the village... The GPS is my watch is pretty accurate and can track when I am walking on different sides of the road, when I cross over, etc. (it has GPS and GLONASS receivers)...
When I walked down the fally-down hill it shows that I have left the road and walked across a field (in reality, it would be in thin air). Of course I haven't it is just that the road has moved so much since the map data was collected!