A major change is coming for America’s mountains, valleys, forests and waters—or, at least, their official locations and sizes. Researchers at the National Oceanic and Atmospheric Administration are nearly finished with a complete overhaul of the National Spatial Reference System (NSRS), the framework that defines where things are and their orientation in space for the U.S. and its territories. The new framework is in beta testing and will be finalized in early 2027. “Every latitude, longitude and height all across the country is going to change a little bit,” says Kevin Ahlgren, a geodesist with the National Geodetic Survey, the agency within NOAA that’s managing the transition.
The new models, which may alter measurements by up to around six feet, reflect actual changes to the environment, such as ice melt, as well as technological and scientific advances since the last update, including the release of GPS. The NSRS’s horizontal component accounts for the slowly spinning, crimping movements of continental plates, which have thrown off latitudes and longitudes since the last model was released in 1986. Vertical changes come down, in large part, to gravity.
Scientists have known for centuries that gravity is not the same everywhere on Earth, and there is a theoretical model, the geoid, that depicts these fluctuations. More massive objects, such as mountains, exert a greater gravitational pull; even in relatively flat areas, geologic differences under the surface can produce bulges of gravity. As Derek van Westrum, a NOAA physicist specializing in a high-precision instrument called a gravity meter, puts it, Earth is a “blobby” place, both physically and gravitationally—as seen in the potatolike geoid.
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Under the new system, scientists are using the geoid to help define the invisible “sea level” from which heights are measured in the NSRS. Over 17 years, research airplanes crisscrossed the country to develop a new gravitational picture based on direct measurements. Scientists combined these data with readings from the ground and from space to produce a comprehensive model of where sea level is at every point in the country—the vertical datum, which was last updated in 1991. Per the new model, elevation above sea level will undergo the smallest shift in the Southeast, and the extent of changes will increase toward the north and west; in Alaska the official height of geographic features may shrink by around six feet.
“It’s a complete change—a new paradigm,” says Demián Gómez, a geodesist at the Ohio State University who has been studying applications of the updated system. More accurate and precise vertical measurements will improve floodplain mapping and models of water flow. National Geodetic Survey scientists say it will also improve surveying and construction, automated navigation, and early-warning systems for earthquakes. These updated coordinates and heights will be used by all federal agencies and for all federally funded projects—and, for the average user, they’ll also be reflected in GPS devices and mapping programs. Mountain peaks and floodplains aren’t going to physically change, but the new system will bring our mode of measuring the world into better alignment with our experience of it.
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