NAD83

NAD83
Name	North American Datum of 1983
Type	Geocentric geodetic datum
Epoch	1986.0 (initial realization)
Ellipsoid	Geodetic Reference System 1980
Usage	Surveying, mapping, navigation across United States, Canada, Mexico, Greenland

NAD83 is a geocentric geodetic datum established to provide a consistent three-dimensional reference frame for position coordinates across North America, Central America, and adjacent oceans. It replaced earlier regional systems to improve compatibility with satellite-based positioning, providing a modern ellipsoidal model tied to the Geodetic Reference System 1980 ellipsoid and realized through networks of ground control and space-geodetic measurements. NAD83 underpins national mapping programs of entities such as the National Geodetic Survey, the Geological Survey of Canada, and the Instituto Nacional de Estadística y Geografía.

Overview

NAD83 defines an Earth-centered, Earth-fixed coordinate system aligned with the International Terrestrial Reference Frame conventions adopted by international bodies like the International Association of Geodesy and the International Earth Rotation and Reference Systems Service, enabling interoperability with systems used by the National Aeronautics and Space Administration, the United States Department of Defense, and civilian positioning services. The datum specifies reference ellipsoid parameters from the Geodetic Reference System 1980 and a fixed origin and orientation tied to observations from satellite tracking networks developed by organizations including the Scripps Institution of Oceanography and the Naval Observatory.

History and development

Development of the datum was driven by incompatibilities between regional datums such as those used by the United States Coast and Geodetic Survey and provincial surveys of Canada and the need to exploit signals from the Global Positioning System. Major contributors included the National Oceanic and Atmospheric Administration, the Geological Survey of Canada, and university research groups such as the Massachusetts Institute of Technology and the University of New Brunswick. Early scientific workshops, NATO-affiliated research collaborations, and technical committees of the International Association of Geodesy informed the transition from classical geodetic triangulation tied to physical monuments toward a satellite-referenced, geocentric realization.

Reference frame definition and realization

The datum is defined by an ellipsoid (GRS 80), a geocentric origin, and orientation and scale parameters that align with the conventional terrestrial reference at a specified epoch. Realizations of the frame were produced by adjustments of extensive terrestrial networks and incorporation of satellite geodesy such as very long baseline interferometry from institutions like the Max Planck Institute for Radio Astronomy and satellite laser ranging operated by observatories associated with the European Space Agency and the International Laser Ranging Service. Agencies including the National Geodetic Survey and provincial survey authorities applied least-squares network adjustment techniques and point velocity models from the United States Geological Survey and the Canadian Geodetic Survey to create practical coordinate catalogs for control stations.

Datums and coordinate systems derived from NAD83

Derived systems include state plane coordinate systems overseen by state-level offices such as the California Department of Transportation and the Texas Department of Transportation, Universal Transverse Mercator (UTM) zones used by mapping agencies like the United States Geological Survey, and provincial projected grids administered by the Ontario Ministry of Natural Resources and Forestry and the Quebec Ministère des Transports. Orthometric height networks tied to NAD83-derived horizontal control are maintained by hydrographic services such as the Canadian Hydrographic Service and the National Oceanic and Atmospheric Administration’s National Geodetic Survey, which produce geoid models for conversion to orthometric heights.

Differences from other datums (e.g., NAD27, WGS84)

Compared with older regional datums such as the datum based on the Clarke 1866 ellipsoid used in the earlier North American system, this datum is geocentric and uses a different ellipsoid (GRS 80), producing systematic coordinate shifts that affected mapping programs of agencies like the United States Forest Service and the Bureau of Land Management. Differences versus the global system maintained as WGS84 influenced interoperability with platforms operated by the United States Department of Defense and civilian services like International Civil Aviation Organization navigation, requiring transformation parameters developed by organizations including the Federal Geographic Data Committee to convert between frames for applications in aviation, maritime navigation, and cadastral surveying.

Realization updates and maintenance (e.g., NAD83(1986), NAD83(CORS96), NAD83(2011))

Initial realization efforts around the 1986 epoch produced coordinate sets used by federal agencies including the National Oceanic and Atmospheric Administration; subsequent realizations incorporated data from continuously operating reference station networks run by entities such as the National Geodetic Survey’s CORS program, international collaborators like the Canadian Geodetic Survey, and research centers at institutions like the Jet Propulsion Laboratory. NAD83(CORS96) and later NAD83(2011) represent epochs and adjustments that integrated Global Navigation Satellite System observations, velocity models from geophysical institutes such as the Pacific Geoscience Centre, and datum transformation parameters published by standards committees including the International Association of Geodesy task forces. Maintenance is performed by national agencies coordinating with academic partners and international services like the International GNSS Service.

Applications and usage in surveying, mapping, and GIS

Federal mapping programs run by the United States Geological Survey and the Natural Resources Canada rely on the datum for topographic mapping, cadastral surveys managed by county recorder offices and land registry agencies, and transportation projects executed by departments such as the Federal Highway Administration and provincial ministries. Geospatial data infrastructures, including datasets hosted by the Geospatial Data Infrastructure of Canada and the National Spatial Data Infrastructure initiatives, use the datum for interoperability across platforms such as GIS products from vendors like Esri and remote sensing processed by centers like the USGS Earth Resources Observation and Science Center. Surveyors accredited through professional bodies such as the National Society of Professional Surveyors adopt realization-specific procedures and transformation grids for precise coordinate work in engineering, utilities, and environmental monitoring projects run by agencies like the Environmental Protection Agency.

Category:Geodetic datums