Including insights on the National Spatial Reference System Modernization.
Written by Raiana Kelly
NAD83, or the North American Datum of 1983, is a geometric datum used as a reference point for mapping and surveying in the United States, Canada, Mexico, and Central America. With the help of satellite technology and using an ellipsoid model of the Earth, NAD83 accounted for latitude, longitude, and ellipsoid height - a significant advancement of accuracy compared to NAD 27, the horizontal datum that preceded NAD83. Since its adoption, NAD83 has been the most commonly used horizontal datum for surveying and mapping in the United States. This guide will help you understand what datums are, how NAD83 is used in global positioning and navigation, updates and recommendations from the National Geodetic Survey, and more.
Datums are the essential piece of information that allow us to define locations on the Earth’s surface. They are reference points that serve to inform coordinate reference systems, the frameworks used to describe geographic position data. Generally speaking, there are two commonly used types of datums: horizontal and vertical.
Horizontal datums, such as NAD83, utilize latitude, longitude, and ellipsoid height to determine specific positions on the earth’s surface. Vertical datums use altitude to collect measurements of land elevations and water depths. Datums are used to create maps, determine property lines, conduct different types of surveys, measure sea levels, and to monitor the movement of the Earth’s crust.
When discussing or reading about datums, you may come across a few different datum classifications: geodetic datums, geometric datums, and geocentric datums. These are simplified terms used to describe the purpose of a particular datum. Depending on where you’re located and what you’re doing, geodetic, geometric, and geocentric datums serve different but related purposes.
Started in 1983 as a collaborative project between the National Geodetic Control Survey of the United States, the Geodetic Survey of Canada, and the Danish Geodetic Institute of Greenland, NAD83 was released in 1986 to standardize geospatial referencing across North America and to upgrade and correct the distortions of its predecessor, NAD27 (North American Datum of 1927).
NAD83 serves as a reference frame for survey professionals, geologists, cartographers, air travel, precision agriculture, utilities, and more. It allows us to accurately map out different locations with the use of GPS technology. When GPS technology and NAD83 is combined with INS applications (inertial navigation systems), it serves as a foundational reference for navigation technology by ensuring consistency and accuracy. The standardization of geospatial referencing is an essential component of guaranteeing consistency and accuracy in geographic data.
NAD83 is the third geodetic datum introduced and was created out of the necessity to make use of the satellite geodetic techniques in surveying and navigation. Before NAD83, there was NAD27 (North American Datum of 1927), a geodetic datum based on the Clarke ellipsoid of 1866, sometimes referred to as the Clarke Spheroid of 1866. NAD27 was established using continental triangulation with a single central origin located at the Meades Ranch in Osborne, Kansas, a historical landmark now known as the “geodetic center of North America,” meaning that the further you move from Kansas, the lower your accuracy will be. With the introduction of satellite geodesy in the 60s and 70s, it became apparent that NAD27 exhibited an “approximately 100 meter offset of the NAD27 origin with respect to the geocenter as well as distortions exceeding tens of meters in some parts of the geodetic control network.” This led to the development of NAD83 and its subsequent adjustments.
The NAD83 reference frame provides accuracy at the one meter level and thus satisfies most practical needs for mapping and navigation where sub-meter accuracy is required. However, as GPS technology advances and the necessity for increased precision becomes more demanding, the requirement for a centimeter level reference frame will also require upgrades to precision geodetic space techniques using VLBI (Very Long Baseline Interferometry
With the widespread adoption of GPS in the late 80s and early 90s, it became clear that the original NAD83 framework was insufficient for professional applications that demanded higher precision. In response, the National Geodetic Survey began making improvements; the first of these was the High Accuracy Reference Network (HARN) and the High Precision Geodetic Network (HPGN) programs.
Beginning in Wisconsin in 1989 and completed in 1998, the HARN program was the first to attempt to create a three-dimensional system with a focus on precise ellipsoid heights in addition to latitude and longitude. The introduction of a vertical component to the datum was a critical step in NAD83’s evolution, and it allowed for the horizontal upgrade of 16,000 survey stations across the United States to A-order or B-order, achieving relative accuracies of 5mm and 8mm, respectively.
While HARN was a necessary response to the inaccuracies of the original NAD83 framework, the decentralized, state-by-state approach created a new challenge: a lack of national consistency. Each state’s network was independently adjusted and constrained, which highlighted the need for a unified, national framework.
The limitations of the HARN adjustments were exposed with the emergence of the Continuously Operating Reference Station (CORS) network. Unlike the passive, monument-based networks of the past, CORS relied on permanently operating GPS receivers to deliver a continuous, steady stream of data.
In response, the National Geodetic Survey launched the NAD83 (NSRS2007) National Readjustment to address the need for a national framework and to integrate the entire passive framework into the CORS network. Using the coordinates of the CORS stations as the control to reposition 67,000 passive monuments, moving away from the state-by-state model of the HARNs and creating a national framework.
While the CORS network served as the foundation for the 2007 adjustment and was a major improvement, it was not without its own inconsistencies. Built using multiple processing techniques, the National Geodetic Survey endeavoured to reprocess the entirety of the CORS network data in a consistent manner. The Multi-Year CORS Solution (MYCS1) resulted in a single, highly-stable active control network that remains the most accurate and reliable version of NAD83 for professional use today.
The NAVD 88 is the official vertical datum of the United States and serves as a consistent and accurate method to measure elevation for mapping, surveying, and engineering projects. NAVD 88 is based on a vast leveling network across the North American continent and incorporates corrections for complex variations in the Earth’s gravity field.
The ITRF is an ECEF (Earth-centered, Earth-fixed) coordinate system that serves as the international standard for a terrestrial reference frame, providing a stable point of reference for the entire Earth. Produced by the IAG (International Association of Geodesy) and maintained by the IERS (International Earth Rotation and Reference Systems), its primary purpose is to provide the necessary accuracy to monitor slow but crucial Earth system processes, such as tectonic plate movement, sea level rise, and melting ice sheets.
Together, NAD83 and NAVD 88 make the National Spatial Reference System, a unified system for geodetic reference in North America. Although still the official horizontal and vertical datums of the NSRS, NGS will be replacing all three NAD83 frames and all current vertical datums, including NAVD 88, with four new terrestrial reference frames and a vertical geopotential datum.
Like the previous iterations of NAD83 and NAD27, the current model has its own shortcomings. According to the NGS, NAD83 is misaligned to the earth’s center by about 2.2 meters and NAVD 88 is both biased by 0.5 meter and tilted by 1 meter coast to coast. Unlike the current system, which relies on a combination of continuously operating GNSS (Global Navigation Satellite System) stations and aging physical survey marks, the modernized NSRS will rely solely on GNSS stations as the primary access points to provide ease of access and maintenance, improved horizontal and vertical accuracies, and responsiveness to geological events such as earthquakes.
As demonstrated throughout this guide, NAD83 has been a foundational element for mapping and surveying in North America since its inception. While it has undergone several significant improvements to enhance its accuracy and utility, advancements in technology and the increasing demand for greater precision continue to drive its evolution. The upcoming modernization of the National Spatial Reference System (NSRS) signifies the next crucial step in providing even more accurate and accessible geospatial referencing for the future.
You can access excellent precision and reliability with Orbitas Correct, powered by Point One Navigation, an RTK (real-time kinematic) technology that takes the guesswork out of your workflow. With Orbitas Correct, you can enjoy automatic corrections applied as you collect without worrying about accessing, choosing, or transforming between datums.
Learn more about Orbitas Correct.
Should I adopt the new NSRS model?
When the new model is finalized, likely in 2026, it is recommended that all organizations that use spatial data should adopt it. The transition will correct longstanding inaccuracies in the existing system and align United States positioning with international standards and modern GNSS technology. The NGS recommends that users transform any data in historic coordinate systems, like those described in this article, to the latest NSRS datums and realization.
How do I transform my data to the new NSRS model?
For Orbitas users, some transformations happen automatically through Orbitas, Orbitas Correct, our partner integration tools, export formats, and custom formats tailored to specific clients. For information about transforming your data in Orbitas, please schedule a professional consultation with an expert at Tri-Global Technologies.
To facilitate transformations independently, the NGS offers the NGS Coordinate Conversion and Transformation Tool (NCAT) and the NADCON 5.0 transformation grids.
If you would like to learn more about transforming your data and converting orthometric heights and other 3D data in ArcGIS Pro, ESRI has provided instructions in an article published this Spring: Prepare Your Data for the National Spatial Reference System Modernization of 2022 in the U.S.
Is NAD83 projected or geographic?
NAD83 is a geographic datum, meaning it uses latitude and longitude to define locations on the Earth’s surface. Projected coordinate systems, in contrast, transform these geographic coordinates onto a flat, two-dimensional plane for mapping purposes.
What is Orbitas?
Orbitas is a mobile data collection application that comes with a web-based management tool. Orbitas allows geospatial professionals across industries to collect, analyze, and manage data in an intuitive and powerful environment.
Users can set up their own coordinate systems, apply custom configurations, store photos, create templates to increase efficiency, perform calculations in the field, and export data into nearly any format needed to integrate with your existing workflow. Orbitas is compatible with all Asteri GNSS receivers, including the Asteri X4i, and can also be used to further enhance your data management in conjunction with other GIS software applications.
What is Orbitas Correct?
Orbitas Correct, powered by Point One Navigation, delivers centimeter-level RTK (real-time kinematic) corrections for GIS, mapping, and survey applications inside of Orbitas. Unlike most RTK services, Orbitas Correct applies corrections automatically inside of Orbitas without users having to sign into an additional service.
For stakers and surveyors that already use Orbitas, that means your workflow is automated and uninterrupted. For geospatial professionals that don’t already use Orbitas, then purchasing Orbitas Correct gives you all the benefits of an Orbitas Basic subscription to expand your asset management capabilities while also applying automatic RTK corrections as you collect.
How much is an Orbitas Correct subscription?
Orbitas Correct requires a Orbitas Basic or Pro subscription. Pricing for Orbitas Correct varies based on your chosen or current Orbitas subscription, with each option featuring a $100 annual discount per Orbitas license. Details of the pricing structure can be found in the table provided below.
What’s the difference between local and ITRF correction datums?
ITRF (International Terrestrial Reference Frame) is a global, dynamic reference frame for accurate positioning using latitude, longitude, height, and time. ITRF relies on a broad network of ground reference stations, offering high accuracy while accounting for the movement of the Earth’s crust. While technically distinct, WGS84 is often aligned with ITRF and is best suited for worldwide applications and GPS.
Local correction datums, such as NAD83 (North American Datum of 1983), are best suited for applications using state survey monuments, such as the DAWG monument where we tested Orbitas Correct.
For applications where precision is critical, a worldwide correction datum such as ITRF or WGS should be used. NAD83 was specifically designed to fit the North American plate, causing its center to be slightly offset from the Earth’s center of mass by roughly 2.2 meters, depending on your location.
Offering the ability to easily switch between local and worldwide datums makes Orbitas Correct an excellent solution for data correction. You can read more about GNSS Accuracy in our 2022 blog post, Asteri X3i and GNSS Accuracy Explained.
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