NAD83

NAD83, the North American Datum of 1983, is a geodetic datum that provides a common reference framework for geographic coordinates in North America. It was developed to replace NAD27 and remains the standard basis for many surveying, mapping, and GIS activities in Canada, the United States, and parts of Mexico.

NAD83 is a geocentric datum defined on the GRS80 ellipsoid, with its origin at the Earth's center of mass. Coordinates such as latitude, longitude, and height are specified relative to this ellipsoid, enabling consistent geographic and projected coordinate systems across the region. The datum underpins a range of map projections, including the various NAD83-based UTM zones and the NAD83 State Plane coordinate systems.

The datum is realized and maintained through networks of ground control points and satellite geodesy, notably GPS. Over time, multiple realizations have been developed to incorporate improved measurements and reference frames. Prominent realizations include NAD83(HARN), NAD83(CORS96), NAD83(2011), and NSRS2007; each aims to provide higher accuracy and better alignment with modern GPS technologies and the ITRF framework. These realizations are not identical and can differ by meters depending on location and epoch.

NAD83 is closely related to, and often compared with, the global WGS84 datum. They are similar in scale and orientation, with differences arising from distinct realization methods and epochs. Transformations between NAD83 and NAD27, or between NAD83 and WGS84, are commonly used in surveying and GIS workflows to maintain consistency across datasets and over time.