The National Geodetic Survey is replacing both national datums. NAD 83 is being replaced by the North American Terrestrial Reference Frame of 2022, and NAVD 88 by the North American-Pacific Geopotential Datum of 2022. This is the largest change to American geodetic practice since NAD 83 arrived, and it is in progress rather than complete.
The motivation is straightforward. Both existing datums were realized before GNSS was ubiquitous, both contain known systematic errors that have been measured but cannot be fixed within their own definitions, and both are anchored to physical marks that move. The modernized system is designed around GNSS and gravity from the start.
What is wrong with the current datums
- NAD 83 is not truly geocentric. Its origin sits roughly 2.2 m from the center of mass of the Earth, so it disagrees with global frames by one to two meters in the horizontal.
- NAD 83 has no built-in, supported way to express motion over time. Epoch handling is a bolt-on rather than part of the definition.
- NAVD 88 is biased from the global geoid by about half a meter and tilted by roughly a meter across the continent.
- NAVD 88 depends on a network of levelled benchmarks, tens of thousands of which have been destroyed, disturbed or displaced by subsidence since they were last observed.
- Maintaining a national levelling network by re-levelling it is no longer economically realistic.
The horizontal replacement
- NATRF2022
- The North American Terrestrial Reference Frame of 2022 — the modernized frame that replaces NAD 83. It is defined by a rotation from the contemporary international terrestrial reference frame, so it is geocentric by construction while still moving with the North American plate.
The design keeps the property surveyors actually want from NAD 83 — a stable point keeps stable coordinates — while removing the property nobody wanted, the offset origin. It does this by defining the frame as an explicit Euler pole rotation applied to the global frame, rather than by fixing a set of station coordinates and letting them age.
Three companion frames cover ground on other tectonic plates: a Pacific frame, a Caribbean frame and a Mariana frame, each defined by its own plate rotation. Together they replace the corresponding NAD 83 realizations for those regions.
Motion that plate rotation does not explain — glacial isostatic adjustment, subsidence, deformation near active margins — is handled by a published intraframe velocity model. That model is part of the system rather than an accessory to it, which is the real structural change.
The vertical replacement
- North American-Pacific Geopotential Datum of 2022
- The modernized vertical datum, defined by the Earth gravity field rather than by a network of benchmarks. Its zero surface is an equipotential surface specified by a conventional geopotential value, and it is accessed through a published gravimetric geoid model.
The practical consequence is a different workflow. Under NAVD 88, the authority is the benchmark and the geoid model is a bridge. Under the new datum, the authority is the geoid model, and an orthometric height comes from a GNSS ellipsoid height minus a modelled geoid height. You get an elevation where you stand, without needing an undisturbed benchmark within levelling distance.
This is only credible because of the underlying gravity work. NGS ran GRAV-D, the Gravity for the Redefinition of the American Vertical Datum project, flying airborne gravity surveys across the United States and its territories for well over a decade specifically to make a centimetre-level gravimetric geoid possible.
What actually changes for a surveyor
| Aspect | Current practice | Modernized practice |
|---|---|---|
| Horizontal frame | NAD 83 (2011), origin offset ≈ 2.2 m | Geocentric plate-fixed frame |
| Time handling | Reference epoch plus HTDP as a separate step | Epoch and velocity model built into the system |
| Vertical reference | NAVD 88, realized by levelled benchmarks | Geopotential datum, realized by a gravimetric geoid model |
| Getting an elevation | Level from a benchmark, or GNSS plus hybrid geoid | GNSS plus gravimetric geoid model |
| Passive marks | Primary source of published control | Supplementary; active CORS stations are primary |
| Coordinate labelling | Often omitted or partial | Frame, epoch and geoid model all required |
Coordinates will change. Horizontal positions will move by one to two meters relative to NAD 83, because that is the size of the origin offset being corrected. Elevations will change by amounts comparable to the NAVD 88 bias and tilt — a decimetre or two in some regions, more than that in others. These are not errors being introduced; they are errors being removed. But every drawing, every GIS layer and every asset database carrying current coordinates will need to be identified as such.
What to do now
- Label everything. Datum, realization, epoch, geoid model, units. This is the single highest-value habit and it costs nothing.
- Record the date of observation with every coordinate, not just the date of the drawing.
- Keep raw GNSS data, not only the derived coordinates. Raw observations can be reprocessed into a new frame; a finished coordinate cannot be recovered.
- Get comfortable with CORS and OPUS workflows, since active stations become the primary access to the frame.
- Talk to clients with long-lived asset databases early. The conversion of a utility or municipal GIS is a project, not a checkbox.
- Do not build systems that assume a coordinate is timeless.
The rollout is being phased and the schedule has moved before. Rather than planning around a date, plan around the properties: a geocentric frame with explicit time dependence, and a vertical datum you reach with a receiver and a model. Practices that already label their data properly and keep their raw observations will find the transition administrative. Practices that do not will find it expensive.