Indicated Accuracy of some Popular Digital Maps
(23 Feb. 2000 -Add Garmin Error Circles, Compared)

The accuracy of these maps can be inferred from a track made in the Atlanta area when SA was turned off for one day on 20 April 1997.  An analysis (HERE) of GPS accuracy on that date indicates the average GPS error was 20 feet.

The maps below show a sizable road error visible in the middle and southern end of the GPS track recorded by a Garmin G-12XL  The first two maps are essentially Tiger-based maps.  The map scales are Approx. 750 feet/inch.

                         Street Atlas 7                                                          Garmin Roads & Recreation
The maps below are based on USGS digital data and show the GPS track closer to the road lines.
                          Garmin USA Topo                                                             Garmin MetroGuide

NOTE: You may check the accuracy of Delorme, Garmin R&R, USA Topo, and Metroguide maps in this same area yourself by using (G7ToWin) to upload the complete track (FILE) to any Garmin receiver.  Then download the track to any of the maps listed above and compare the track plot on them to the maps.

Error Circles Compared Between MapSource R & R,
USA Topo, and MetroGuide Maps in the Garmin G-III+ and StreetPilot
(Tests conducted in the Simulator Mode)
Garmin Roads & Recreation
Garmin USA Topo
Garmin MetroGuide SP (Screen reduced to sizes above)

Jack Yeazel