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Why NAD27 vs NAD83 Matters for US Surveys
The shift from NAD27 to NAD83 introduces 10 to 100+ metres of horizontal offset depending on location. CONUS shifts typically average 20—0m; Hawaii can exceed 100m. NGS's NADCON grid files (conus.las / conus.los) are the accepted national standard (EPSG method 9613) with accuracy ~0.15m.
Even NAD83 vs modern WGS84 introduces ~1—m of offset due to North American plate motion (~15mm/yr). For centimetre-grade work, NGS's HTDP tool is required to resolve epoch-specific positions in ITRF/WGS84 frames. Treating NAD83 = WGS84 is only valid at ±2m accuracy (EPSG op 1728).
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The $50,000 Geodetic Drift Liability: NAD83 vs WGS84
Because the North American Plate moves ~2cm/year, NAD83(2011) and WGS84(G1762) currently diverge by over 2.2 meters. Using a "standard" GPS WGS84 coordinate for a high-precision NAD83 cadastral staking has triggered $50,000 Professional Liability claims for foundational rework and utility misplacement.
Risk Exposure Metric:
2.2-Meter Tectonic Drift & Epoch Accumulation
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Warning: Verify Your Calculation
Coordinate accuracy varies by device and datum. Do not use these results for legal or construction purposes without checking:
GPS Accuracy Alert
Your phone's GPS can be off by 30 meters. This can cause critical errors in your data.
Check My Accuracy →Datum Shift Risk
Using the wrong coordinate system (e.g. WGS84 vs NAD83) creates a permanent 1-meter offset.
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