I've never been teleported 300 feet in another direction in a GPS in six years of using unless I'm in a deep bridge or tunnel. However, do you know what a 1 percent difference is? If your real speed is 10MPH a one percent difference is 10.1 MPH. Or on a 100 mile ride, it's 1 mile off. My GPS is well within 1 percent because I know almost exactly when it's going to reach 3.00 miles right around the stop sign. Considering that I don't ride in a perfect straight line, it varies by about 30 to 50 feet.

And what national map do you use? I own NGS maps, Delorme maps, Delorme Topo, and Mapsource national maps.

All of the Garmin handheld units will fill in any data missing by the GPS, it's not just unique to the Edge series.

I'll upload later today 100 rides I have taken along the same road that is covered in forest land since I can merge them all together. Out of the 100 miles I have ridden, not once has it varied by more than 50 feet.