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# National Water Information System
# 2024/12/22
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# Date Retrieved: USGS Water Data for the Nation Help System
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gw_ref_cd	gw_ref_ds
1s	71s
A	Altimeter.
D	Differentially corrected Global Positioning System.
F	Survey-grade GPSF
I	Interferometric Synthetic Aperture Radar, airplane
J	Light Detection And Ranging, airplane
L	Level or other surveyed method.
M	Interpolated from topographic map.
N	Interpolated from Digital Elevation Model
R	Reported method of determination.
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