Tom Anderson wrote:
"Tom Anderson" wrote in message
h.li...

While pondering the nature of southwest London, i turned to
OpenStreetMap:
http://openstreetmap.org/

The fact that it's a straight line makes me suspect it's based on a
simple error or glitch: someone meant to enter a road linking (eg)
points 100 and 734327, but typed 734372 for the end, which happens to
be rather far way. Possibly the sort of thing some simple validation
steps would catch.

If data was hand-entered in this way there would be such errors all over the
shop. I imagine it's actually caused by a GPS error, where a GPS unit
suddenly thought it was in Portugal for a few seconds, and the user didn't
check before submitting the data.