Altitude method Type Codes
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# National Water Information System
# 2024/11/13
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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