Every official latitude, longitude, and elevation published in the United States will change by up to four meters. The terrain described will not have moved at all. What is being replaced is the reference system from which those numbers are counted. The National Geodetic Survey is retiring the 1983 North American datum and the 1988 North American vertical datum. Those are the horizontal and vertical reference systems that currently underpin surveying, flood mapping, construction and aviation across the country. In their place will come four new terrestrial reference frames and a new geopotential datum. The agency has maintained the national reference system since its predecessor, the Survey of the Coast, was founded in 1807. The reference surface is what is changing. Nothing changes physically. The corner of a property in Ohio will be exactly where it was before, and a mountain in Colorado will be exactly as tall. A coordinate is not a property of a place; It is a measurement of that location against an agreed upon reference surface. The United States is changing the reference surface. Four meters is the interval between two descriptions of the same stationary point. This figure is not uniform either and the organization does not present it as a single national number. Its guide says that the magnitude of the change depends on what data a user is currently working on, what part of the country they are in, and what time the new coordinates refer to. Four meters is the outer edge of the range. NGS publishes separate maps for ellipsoid height change, orthometric height change, and horizontal change on the North American and Pacific plates. Bugs older than NGS satellite navigation give several reasons for the change, including alignment with international standards and with satellite systems orbiting the center of the Earth. Two of the reasons are systematic errors built into systems that were defined before satellite positioning was routine. The first is horizontal. NAD 83 was fixed when the center of the Earth could not be located with the subsequently supplied precision satellites, and its origin was not located where the center of the Earth is now understood to be. The agency’s summary puts the misalignment at about 2.2 meters. NGS gives two different figures for that misalignment on the same page. Its initial summary says about 2.2 meters. A later section says that the origin of the current NAD 83 frames disagrees with international estimates of the Earth’s center by two to four meters, depending on which frame you refer to. There are three NAD 83 frames, which may explain the extension, although the page does not reconcile the two statements. The smallest figure is the one the agency leads with. The second error is vertical. NAVD 88 is the surface from which US elevations are measured. NGS describes it as skewed, about half a meter, and tilted, about one meter, from coast to coast, relative to the best global geoid models currently available. An elevation in Maine and an elevation in Oregon are not measured by the same zero. Elsewhere, the page states what appears to be the same comparison as a single range, with the zero-elevation surface implied by NAVD 88 disagreeing with current estimates of the geoid by about half to two meters. A gravity map flown over the entire country Correcting the vertical error meant measuring gravity, because the surface elevations that are counted are defined by gravity, which does not mark anything visible. That was the work of Gravity for the Redefinition of the American Vertical Datum, a project that collected aerial gravity readings across the United States. Those readings were included in the time-independent component of a geoid model called GEOID2022. That component is a static surface that represents the geoid at the reference epoch 2020.00, while the model on which the modernized system is based is itself time-dependent. GEOID2022 defines the zero orthometric height surface of the new vertical datum, the North American and Pacific Geopotential Datum 2022, which will replace all existing geodetic vertical datums in the system, not just NAVD 88. Frames that rotate with their plates The horizontal side is handled differently. There are four frames, one for each of the four tectonic plates: North America, Pacific, Caribbean and Mariana. Each is named after its plate and will rotate at the average speed of that plate, so latitude and longitude in the stable interior of a plate should shift less with time than they would otherwise. All four will be defined according to the 2020 International Terrestrial Reference Framework. From a million brass disks to a constellation The current arrangement is based on physical objects. NGS describes the existing system carried out through more than 1,000 satellite stations in continuous operation along with an ancient network of more than 1,000,000 survey marks placed on the ground. Those marks are the disks that hikers find on summits and surveyors search for in ditches. NGS’s own description is that they are often deteriorated, destroyed or unmaintained, leaving the heights and positions attributed to them obsolete and inaccurate. The modernized system moves control from the ground to orbit. Access will be primarily through the NOAA and International GNSS Service’s network of reference stations, and NGS calls this a paradigm shift to reach the system by physically occupying a survey mark. The marks do not disappear from the record. They will continue to carry published coordinates and surveyors will still be able to provide satellite data collected about them. Published positions will take an epoch, because an undated position ceases to have meaning in a system precise enough to see the continent move. NGS says it continues to plan for the first reference epoch to be 2020.00. As for sharing, the agency pages currently disagree. A response to the FAQ says that shared user solutions, in which surveyors publish their own calculated positions, will not be supported because those solutions were never integrated with official coordinates. The same FAQ also says that users will be able to share solutions, and the Track Our Progress page that the FAQ points to says that OPUS-Share will be preserved with the caveat that a shared solution should not be used as a geodetic control. The contribution itself does not end. An updated version of the agency’s static processing service will continue to accept user satellite data, and NGS will calculate and publish the resulting coordinates. The timeline has already been pushed back once. The change has not happened yet. In 2020, the agency published a Federal Register notice saying launch was expected between 2022 and 2025. In October 2024 it published another, revising it to 2025 or 2026. That notice also laid out the sequence: components released for public testing, at least six months of testing after the last one landed, then a vote by the Federal Geodetic Control Subcommittee to approve the new system. He called that vote likely in 2026, and the agency’s guidance narrowed it to mid-2026. Mid-2026 has passed, although the warning window has not. NGS said it would mark the milestones with more Federal Register notices: one in late 2025 announcing that all components were available for testing, and another in 2026 after an approval vote. You can look up exactly that in the Federal Register. National Oceanic and Atmospheric Administration notices mentioning the National Spatial Reference System, published since June 2024, appear as three documents. Only one of the three refers to the reference system, and that is the October 2024 notice itself. None of the promised notices appear to have been published. Until the post-vote notice is published, NAD 83 and NAVD 88 remain the official US data. The names will not be adjusted to match the year the system actually arrives. Each component has 2022 in its title, and NGS has said it intends to keep those names, arguing that the year has no scientific meaning and the terms have been public for years. He points out that this has happened before. NAD 83 was published in 1986 and NAVD 88 in 1991. The deadline is already on the calendar. Geodetic survey projects that create or update control in the current system must reach NGS by January 13, 2027, and the agency will not accept new submissions after that date. Existing software remains available until the modernized system is fully implemented, but no new work enters the old record. The agency’s explanation is more procedural than dramatic: The modernized system requires new databases, workflows, software products and services that differ from the current ones. What follows is a slower legal solution. The NGS FAQ interprets the Geospatial Data Act of 2018 as requiring federal civilian agencies that collect, produce, acquire, maintain, or disseminate geospatial data to use the new frameworks within five years of their adoption by the Federal Geographic Data Committee. The same FAQ says that any state agency or organization that receives federal funds to generate or process geospatial data must comply; others, it says, must follow applicable state or local laws or contract terms. Some states may need to have their statutes changed, and for them, the surveying organizations and NGS jointly drafted model legislation, written vaguely enough to reference the most recent data and not name any, so that the same fight need not happen again. Flood insurance rate maps are located downstream of the vertical datum, and NGS ran a pilot with FEMA in North Carolina as early as 2010 to find out what a new elevation surface would do to them. What is being replaced is an agreement on where zero is and from what point in space each number published in the country is counted. The agency’s own notice calls NAD 83 and NAVD 88 the last significant modernization and says that no significant upgrade was possible so far. The disks on the ground will remain where they are, still carrying coordinates, but the system will no longer be accessible by kneeling on top of one. About this articleThis article is for general information and reflection. It is not professional advice. For your specific situation, consult a qualified professional.
