there is also the accuracy of your reciever at any point in time to remember about......
I have noticed on google maps "out in the wilds of Northern Scotland" there are chunks they still haven't managed to get a clear day for a decent photo.
if you look closely at the join, not all the roads etc line up perfectly, so always treat with a small pinch of salt. I read somewhere that it's best to assume a worst case
accuracy of around 30m radius, although that might have been Streetmap on the 1:50K sheets.