"Typhoon502" writes:
My satnav is configured to give me a dot indicating the actual GPS
placement along with the directional arrow that the system software
snaps to the road that it thinks you're on (this is how most car
systems work), and you'd be surprised at how often the map data isn't
quite correct. A section of Rt. 50 in DC Metro is mapped offset
probably 100 feet from where the road actually is, for example...my nav
would show me on the wrong side of the divided 6-lane for about 1/4
mile or so.

I drove up to Prince Edward Island over the holidays. For the first
10km or so of driving over the Confederation bridge my GPS was
convinced I had turned my car into a boat and was driving through the
Atlantic ocean about 1km west of the bridge... It was quite amusing
to watch. (And no, it was not a temporary glitch -- I saw the same
error on the return trip.)

Chris