NAD27 / NAD83 / WGS84 Risk Validator
Validate coordinate compliance against US national geodetic standards. Detect NAD27→NAD83 shifts (10–100m regionally), assess NAD83→WGS84 epoch drift (~1–2m), and classify risk per NGS / NOAA regulatory mandates.
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 20–40m; 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 ~1–2m 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).
→ Read the Full USA Datum Authority Guide