Per-section mean 1-sigma horizontal accuracy varies from better than 0.7 meter (California A,L-O) to a max of 3.8 meters for Oregon G. The mean accuracy over the entire trail is 1.9 meters. In general, the error values are low when there is no tree cover and are much higher under trees -- and worst of all when trees are coupled with steep terrain. All data has been filtered and then reduced for GPS compatibility.

A few side trails have been created solely by reference to satellite imagery and maps. Those accuracies are unknown and are not factored into the statistics above.

Elevation values are spline-interpolated from hundreds of surrounding 1/3 arcsecond USGS DEM grid points and, as such, are NAVD88-based (i.e., they are quasi-MSL).