Commercial-grade technology has about 3m accuracy, but different methods can yield down to 10cm accuracy: https://en.wikipedia.org/wiki/Global_Positioning_Syst

Commercial-grade technology has about 3m accuracy, but different methods can yield down to 10cm accuracy: https://en.wikipedia.org/wiki/Global_Positioning_System#Precise_monitoring https://en.wikipedia.org/wiki/Global_Positioning_System#Prec... And then there's a whole segment of survey-grade equipment that can get within a centimeter or two: http://water.usgs.gov/osw/gps/ http://water.usgs.gov/osw/gps/