It's not so much that things are not quite on top, it's that there is a distinct offset, on the 1:50000 mapping, which isn't on the base map (vector map I think), or Google Maps (via Bikely). I noticed yesterday on the way home, that cycling along some London streets, where there are a bunch of parallel roads, the GPS in effect said I was on a road adjacent to the one I was on. It was fairly obvious, since I know the road, and the one I was actually on has a turning that the one the GPS said I was on doesn't, but conceivably you could come a bit unstuck if you didn't know the area. Of course, the Active 10 isn't really meant for use in an Urban environment, and is more at home in the open countryside, where this would probably be less of an issue.