NAD83 Explained
NAD 83 explained — US federal horizontal datum on GRS80, plate-fixed to North America, ~1-2 m offset from WGS-84 in CONUS, and replaced by NATRF2022 in 2025-2027.
By Steve K.. Published . Last updated .
NAD 83 is the official horizontal geodetic datum of the United States, Canada, Mexico and Central America. It is fixed to the North American tectonic plate, so coordinates within North America stay numerically stable as the plate drifts; the current realization is NAD 83(2011), epoch 2010.00.
NAD 83 is the official horizontal datum of US federal mapping, every state cadastral system, every USGS quadrangle, and most North American infrastructure records. The wider datum picture is covered by /learn/what-is-a-geodetic-datum, and the global GPS-broadcast counterpart by /learn/wgs84-explained. Its key difference from WGS-84 is that it's plate-fixed: coordinates within North America don't drift as the continent moves. This pillar covers the NAD 83 specification, its seven realizations since 1986, the relationship and offset to WGS-84, the 2025-2027 NSRS Modernization that will replace it, and the operational implications for surveying and federal data integration.
What NAD 83 is
NAD 83 is a geocentric datum based on the GRS80 ellipsoid, fixed to the North American tectonic plate so that points on the plate keep stable coordinates as the plate moves.
| Component | NAD 83 value | Source |
|---|---|---|
| Ellipsoid | GRS80 | Moritz (2000) |
| Semi-major axis (a) | 6,378,137 m (exact, same as WGS-84) | GRS80 / IAG |
| Reciprocal flattening (1/f) | 298.257222101 | GRS80 |
| Origin | Earth's centre of mass (geocentric) | NAD 83(1986) onward |
| Fixed to | North American tectonic plate | Plate-fixed convention since NAD 83(1986) |
| Initial realization epoch | 1986.0 | NAD 83(1986) |
| Current operational realization | NAD 83(2011), epoch 2010.00 | NOAA NGS |
| Successor (in flight) | NATRF2022, epoch 2020.0 | NSRS Modernization rollout |
The GRS80 ellipsoid is almost identical to the WGS-84 ellipsoid: both have a = 6,378,137 m exactly, and their flattenings agree to the 8th decimal place. The metre-scale offset between NAD 83 and WGS-84 comes from the datum difference (which reference frame the coordinates are expressed in) — not the ellipsoid difference.
The realizations of NAD 83
The NAD 83 definition has been stable since 1986, but the realization (the network of stations whose coordinates are authoritatively NAD 83) has been re-derived several times.
| Realization | Year | Technique | Approximate accuracy | Status |
|---|---|---|---|---|
| NAD 83(1986) | 1986 | Triangulation + Doppler satellite | ~0.5-2 m vs WGS-84 at the time | Superseded |
| NAD 83(HARN) / HPGN | 1989-1997 by state | High-Accuracy Reference Network; campaign GPS | ~5-10 cm at NGS control points | Superseded |
| NAD 83(CORS96) | 1996-2002 | CORS network observations | ~1-3 cm at CORS stations | Superseded |
| NAD 83(NSRS2007) | 2007 | CORS network observations + reanalysis | ~1 cm | Superseded |
| NAD 83(2011) | 2011 | CORS network observations; epoch 2010.00 | ~1 cm at CORS stations | Current operational |
| NATRF2022 (successor) | 2025-2027 | Multi-GNSS + space geodesy; aligned to ITRF | Sub-cm | NSRS Modernization rollout |
Each realization is a new fit to the network of NAD 83 control points using the best available measurements at the time. The re-fits don't change the datum's definition (still GRS80, still geocentric, still plate-fixed) but they correct station positions to higher precision.
Why plate-fixed vs geocentric matters
The crucial difference between NAD 83 and WGS-84 is what they're attached to.
| Property | NAD 83(2011) | WGS-84(G2139) |
|---|---|---|
| Attached to | North American tectonic plate | Earth's centre of mass (global average) |
| Coordinates of fixed monuments | Stay numerically constant over time | Drift ~2-3 cm/year (plate motion) |
| Coordinates of a fixed building (e.g. White House) | Same number in 1990 and 2030 | Different by ~80 cm-1 m between 1990 and 2030 |
| Best for | Long-term records: deeds, cadastre, infrastructure monumentation | Real-time GPS, global data exchange, web mapping |
| Offset to other datum (CONUS, 2026) | (baseline) | +1-2 m east of NAD 83(2011) coordinates |
For a US property deed recorded in 1990, the NAD 83 coordinate is the same in 2030 because the deed's reference monument has stayed at the same numerical NAD 83 coordinate even though the monument itself has drifted ~80 cm eastward in absolute terms with the continent. A WGS-84 coordinate for the same monument has changed by ~80 cm over the same period. NAD 83 is therefore the right choice for cadastral records; WGS-84 is the right choice for GPS-derived positioning.
The WGS-84 ↔ NAD 83 offset
The two datums were intentionally aligned in 1986 to agree at the centimetre level at GPS reference stations. Since then, the North American plate has drifted relative to the global geocentric frame by ~2-3 cm/year, and the cumulative offset is now ~1-2 m in CONUS.
| Location | WGS-84(G2139) ≈ NAD 83(2011) offset (2026) | Direction | Note |
|---|---|---|---|
| CONUS centre (Kansas) | ~1.0-1.5 m | East | Typical CONUS value |
| Pacific Northwest (Seattle) | ~1.2-1.7 m | East | Mid-CONUS scale |
| New England (Boston) | ~0.8-1.2 m | East | Smaller offset |
| Alaska (Anchorage) | ~3-4 m | East-southeast | Near plate boundary |
| Hawaii (Honolulu) | ~1.5-2 m | Various | Pacific Plate, not North American |
| Southern California (LA) | ~2-3 m | East | Near San Andreas Fault |
The offset grows over time as the North American plate continues drifting. The 1-2 m value is a typical 2026 number for CONUS interior. Surveying work that needs sub-metre WGS-84 ↔ NAD 83 conversion must use NGS NCAT (the authoritative US service) or the PROJ library with current parameter sets.
The CORS realization network
NAD 83(2011) is realized through the Continuously Operating Reference Stations (CORS) Network: ~1,800 permanent GNSS stations across the US (plus partner stations in Canada and Mexico) whose positions are known in NAD 83(2011) to centimetre accuracy.
| CORS property | Value | Source |
|---|---|---|
| Number of stations | ~1,800 (US); ~3,000 across North America with partners | NOAA NGS |
| Station density | ~1 per 100 km in densely surveyed regions; 1 per several hundred km in remote areas | NGS |
| Station accuracy | Sub-centimetre in NAD 83(2011) | CORS data sheet |
| Update cadence | Daily processed solutions; final at 14 days | NGS |
| Public availability | Free; downloadable RINEX data | cors.ngs.noaa.gov |
| Operating since | 1994 (initial CORS) | NOAA NGS history |
| Use cases | Survey-grade RTK base, post-processing reference, datum maintenance | NGS |
Survey-grade GNSS in the US generally references CORS data for post-processing or real-time corrections. A surveyor in the US can reach 1-2 cm horizontal NAD 83(2011) coordinates by combining their field GPS observations with the nearest CORS station's reference data via the OPUS (Online Positioning User Service) workflow.
NSRS Modernization: NATRF2022 (in flight)
NOAA NGS is replacing NAD 83 (and NAVD 88 vertical) with new frames on a 2025-2027 rollout.
| New frame | Replaces | Key change | Alignment to |
|---|---|---|---|
| NATRF2022 (horizontal) | NAD 83(2011) | New realization aligned more tightly to ITRF and WGS-84 | ITRF2020 / WGS-84(G2139) |
| NAPGD2022 (vertical / geopotential) | NAVD 88 | Gravity-based, no tide-gauge anchor | Hybrid geoid |
| Pacific frame | No predecessor (Pacific plate added) | Covers Hawaii, Guam, American Samoa | ITRF2020 |
| Caribbean frame | No predecessor (Caribbean plate added) | Covers Puerto Rico, USVI | ITRF2020 |
| Mariana frame | No predecessor (Mariana plate added) | Covers Mariana Islands | ITRF2020 |
The successor system has 4-5 separate horizontal frames because the USA spans several tectonic plates (North American, Pacific, Caribbean, Mariana, plus tributary structures). Each frame is plate-fixed for its region; the boundaries between frames have to be handled explicitly. This is more complex than NAD 83's single-frame approach but more accurate for cross-plate work.
Operational implications
| Use case | Datum | Why | |---|---|---| | US property deeds, cadastre | NAD 83(2011), per state requirements | Stable coordinates over decades | | USGS topographic maps | NAD 83(2011), eventually NATRF2022 | Federal standard | | Civil engineering plans | NAD 83 (state plane) | Survey-grade coordinates with plate-stable reference | | Real-time GPS in a vehicle | WGS-84(G2139) | Direct broadcast; no transformation overhead | | GeoJSON / web mapping | WGS-84 (EPSG:4326) | Universal default | | Cross-system data (federal NAD 83 + GPS WGS-84) | Convert via NGS NCAT | The 1-2 m offset matters for survey-grade work | | Plate tectonics research | ITRF realizations | Global geocentric frame | | Long-term infrastructure records (highways, pipelines, utilities) | NAD 83 → NATRF2022 when adopted | Plate-stable preserves geometric relationships |
Common misconceptions
Related
- WGS 84 Explained— The global counterpart datum used by GPS
- WGS 84 vs NAD83— How and why the two datums diverge over time
- What Is a Geodetic Datum— The pillar covering what datums are and why they matter
- Datum Transformations— How to convert coordinates between datums
- NSRS Modernization— The NSRS2022 replacement for NAD83 currently underway
- The State Plane Coordinate System— The US per-state projection system built on NAD83
- Methodology— How content is sourced and verified
Frequently asked questions
What is NAD83?
The North American Datum of 1983 is the standard horizontal geodetic datum for North America. It is the reference frame used for nearly all surveying, mapping, GIS, and engineering work in the United States, Canada, and Mexico. NAD83 uses the GRS80 ellipsoid (Geodetic Reference System 1980), which is geometrically virtually identical to the WGS84 ellipsoid — the semi-minor axes differ by about 0.1 mm.
How does NAD83 differ from NAD27?
NAD27 — the North American Datum of 1927 — used the Clarke 1866 ellipsoid and was anchored at Meades Ranch, Kansas. NAD83 uses the GRS80 ellipsoid and is geocentric (centred at Earth's centre of mass) rather than fitted to a specific point. The change from NAD27 to NAD83 shifts coordinates by tens of metres at any given point in the US — about 30 m on average, growing to over 100 m in some areas. Conversion between the two requires specific transformation tools (NADCON in the US, GSRUG in Canada).
Why has NAD83 diverged from WGS84?
Plate tectonics. NAD83 is anchored to the North American Plate, which is rotating and translating relative to Earth's centre at about 2.5 cm per year. WGS84, by contrast, is anchored to the International Terrestrial Reference Frame (ITRF) and tracks Earth's centre of mass independent of any plate. The two datums were aligned in the mid-1980s, but the North American Plate has drifted southwest of its 1986 position, so coordinates expressed in NAD83 now differ from the same physical point expressed in WGS84 by about 1-2 metres in the conterminous US. The gap grows by about 2.5 cm per year.
What are the multiple realizations of NAD83?
Each major improvement in geodetic measurement has produced a new 'realization' of NAD83 — a refined set of station coordinates that more accurately represents the underlying datum. The major realizations are NAD83(1986) (original), NAD83(HARN) state-by-state (High Accuracy Reference Network, ~1990s), NAD83(CORS96), NAD83(NSRS2007), and NAD83(2011). Each can shift point coordinates by centimetres to a few decimetres. The upcoming NSRS2022 modernisation will replace NAD83 entirely with new datums (NATRF2022 for terrestrial, NAPGD2022 for vertical). Surveyors must specify which realization their data uses.
When does it matter which datum you use?
It matters for any work where 1-2 metres of horizontal precision is meaningful: cadastral surveys, engineering design, infrastructure planning, precise agriculture, scientific monitoring. It does NOT matter for consumer GPS receivers (which use WGS84, with the user generally unaware), most navigation, recreational mapping, and casual location-sharing. The rule of thumb: if your work uses survey-grade GPS or any survey monument coordinates, know which datum and which realization. If your work uses a smartphone or a typical consumer device, you are getting WGS84 and the NAD83/WGS84 difference is below your accuracy.
What is NSRS modernization?
NSRS Modernization is NOAA NGS's 2025-2027 replacement of NAD 83 and NAVD 88 with new reference frames: NATRF2022 (North American Terrestrial Reference Frame 2022) horizontally, and NAPGD2022 (North American-Pacific Geopotential Datum 2022) vertically. The new frames are aligned far more tightly with WGS-84 and ITRF, and they split the US into 4-5 plate-specific frames (North American, Pacific, Caribbean, Mariana). Legacy NAD 83 data will need explicit transformation.
How do I convert NAD 83 to WGS 84?
Use NOAA NGS's NCAT (National Coordinate Conversion and Transformation Tool) online or PROJ in code. The typical CONUS offset is 1-2 metres but varies by location and the specific NAD 83 realization (1986, 2011, HARN, etc.). Coordinates must specify which realization they're in — "NAD 83" alone is ambiguous. PROJ supports EPSG:6318 (NAD 83(2011) geographic) and EPSG:4269 (NAD 83 generic) as separate identifiers.
Is NAD 83 the same as WGS 84?
No — but they're close. Both use ellipsoids with the same semi-major axis (6,378,137 m); they differ only in the 8th decimal place of 1/f. The crucial difference is the *datum* anchoring: WGS-84 is global (Earth-centre-of-mass), NAD 83 is fixed to the North American plate. In CONUS the two diverge by ~1-2 metres today, growing ~2-3 cm/year. For sub-metre work the distinction matters; for consumer GPS it's below noise.
Sources
- NOAA NGS — National Geodetic Survey — datums and reference frames · https://geodesy.noaa.gov/datums/index.shtml · Accessed .
- NOAA NGS — Continuously Operating Reference Stations (CORS) · https://www.ngs.noaa.gov/CORS/ · Accessed .
- NOAA NGS — National Spatial Reference System (NSRS) modernization · https://geodesy.noaa.gov/datums/newdatums/index.shtml · Accessed .
- NOAA NGS — HTDP — Horizontal Time-Dependent Positioning · https://geodesy.noaa.gov/TOOLS/Htdp/Htdp.shtml · Accessed .
- NGA — World Geodetic System 1984 (NGA.STND.0036) · https://earth-info.nga.mil/index.php?dir=wgs84&action=wgs84 · Accessed .
- USGS — The National Map — geodetic context · https://www.usgs.gov/programs/national-geospatial-program/national-map · Accessed .
Cite this article
APA format:
Steve K. (2026). NAD83 Explained. Coordinately. https://coordinately.org/learn/nad83-explained
BibTeX:
@misc{coordinately_nad83explained_2026,
author = {K., Steve},
title = {NAD83 Explained},
year = {2026},
publisher = {Coordinately},
url = {https://coordinately.org/learn/nad83-explained},
note = {Accessed: 2026-06-05}
}