# # National Water Information System # 2024/12/04 # # # Date Retrieved: USGS Water Data for the Nation Help System # gw_ref_cd gw_ref_ds 1s 71s C Calculated from land net D Differentially corrected Global Positioning System. W GNSS1 - Level 1 Quality Survey Grade Global Navigation Satellite System X GNSS2 - Level 2 Quality Survey Grade Global Navigation Satellite System Y GNSS3 - Level 3 Quality Survey Grade Global Navigation Satellite System Z GNSS4 - Level 4 Quality Survey Grade Global Navigation Satellite System N Interpolated from Digital MAP. M Interpolated from MAP. L Long range navigation system. G Mapping grade GPS unit (handheld accuracy range 12 to 40 ft) R Reported. F Survey-grade GPSF S Transit, theodolite, or other surveying method. U Unknown.