Surveyors Prepare: Datums are Changing!

WHO: The  National Geodetic Survey  (NGS), located within the National Oceanic and Atmospheric Administration (NOAA) of the United States government.  The NGS is responsible for defining, maintaining, and providing access to the country’s positioning infrastructure called the  National Spatial Reference System  (NSRS).

WHAT: Is  updating the NSRS  - horizontal (geometric, NAD 83) and vertical (geopotential, NAVD 88 and local island vertical datums PRVD02, USVI09, ASVD02, GUVD04, HAWAII - Local Tidal) geodetic datums, an effort that has been underway since 2007.

WHERE: The North American, Pacific, Caribbean, and Marianas plates.

WHEN: Now - rollout is underway. An updated  Federal Register Notice  was released in October 9, 2024.   Alpha  and  Beta  products are being released, with full replacement of the NSRS anticipated in 2026.

WHY: These datums have been in use since GPS was in its infancy – i.e., for decades, and there are known limitations that the new system addresses:

• NAD 83 is not as geocentrically defined as today's positioning technologies demand, meaning not referenced to the center of Earth’s mass – by about 2.24 meters based on the latest international estimates. This is problematic when using Global Navigation Satellite Systems (GNSS), which orbit about and provide positions relative to the center of the Earth.
• NAD 83 grouped the North American and Caribbean plates in its definition.  The updated system has broken those two plates out (because we now understand how to measure how the plates rotate individually) in addition to the Pacific and Marianas plates included in NAD 83, resulting in definitions for four Terrestrial Reference Frames (TRFs): NATRF2022, PATRF2022, MATRF2022, and CATRF2022.
• Continental drift and vertical land movement were not accounted for in the existing NSRS.  Reference epochs (timestamps, for instance) for coordinates have been introduced for survey data to help us better understand movement or change over time.
• Based on current international estimates of the geoid, NAVD 88 is biased by approximately 1.5 meters and tilted 1 meter coast-to-coast.
• There are currently multiple vertical datums.  The new system will consist of one.
• NAD 83 and NAVD 88 were designed independently, resulting in reduced accuracy.  In the new system, they were designed together resulting in better integration and higher accuracy.
• GEOID 18 and previous models were hybrid models “warped” to match leveled bench marks. GEOID2022 will be a more consistent and stable model as it is a purely gravimetric geoid model.
• Currently, both physical marks and continuously operating GNSS stations are relied upon for the existing NSRS. Physical marks become degraded and destroyed over time negatively impacting height and position data. The modernized NSRS will rely exclusively on GNSS stations.
• State Plane Coordinate System 83 (SPCS 83) includes high levels of distortion for many areas. The modernized SPCS2022 minimizes the distortion or scale error (difference between ground and grid measurements) at the topographic surface rather than the reference ellipsoid surface and is designed to minimize distortion in populated or areas of high use.
• An important change between SPCS 83 and upcoming SPCS2022 is that only the international foot (1 foot = 0.3048 meter, exactly) will be supported, which differs from SPCS 83 with some states officially using the international foot while others use the U.S. survey foot (1 foot = 1200/3937 meters). This is consistent with the  deprecation of the U.S. survey foot  initiated by the National Institute of Standards and Technology (NIST) the end of December 2022.

HORIZONTALLY: Keep in mind NAD 83 will remain valid, and not all existing maps and geospatial data will need to be transformed. Also, the use of specific datums is set forth by individual state statutes; statutes that will need to be updated by each state to reflect the coming change in datums (for guidance, see the next section "How to Prepare for NSRS Modernization.")

The current three NAD 83 datums (frames) will be replaced by NATRF2022 consisting of four new terrestrial reference frames (TRFs) (Figure 1). The new TRFs are "plate fixed" meaning that each is tied to a specific tectonic plate and accounts for that plate's rigid motion, resulting in a higher level of coordinate consistency over time.

Just like the current NAD 83 datums (frames), the new horizontal “datums”, more precisely referred to as Terrestrial Reference Frames (TRFs), will support measurements of latitude, longitude, and ellipsoid height, such that the term “horizontal” is a bit misleading.  However, that is likely how software and other platforms will continue to label it.

For data that need to be transformed to the new reference frames surveyors should be aware of the anticipated magnitudes of coordinate shifts and the uncertainty that this transformation will add, or at a minimum what changes to expect when working in the updated NSRS.

As noted in the Overview section, the Earth's origin will shift by ~2.4 meters (Figure 2) resulting in shifts of up to several meters horizontally (Figure 3) and up to 1.7 meters in ellipsoid height (Figure 4) in the conterminous U.S.

Transformed coordinate accuracy must be evaluated accordingly, as all transformations introduce some level of uncertainty. There may be instances where reprocessing or readjusting the original survey data in the new reference frames may be preferred. Or, if the uncertainty cannot be measured or is outside of acceptable limits, creating datasets with new observations may be the best option to meet your requirements.

VERTICALLY: Like NAD 83, NAVD 88 and the local island vertical datums noted previously will remain valid datums and not all existing maps and geospatial data will need to be transformed to the  North American-Pacific Geopotential Datum of 2022 (NAPGD2022) . For data that do need to be transformed, shifts of up to 1.5 meters vertically in the conterminous U.S. can be expected (Figure 5). The same applies for vertical transformations as horizontal - all transformations introduce some level of uncertainty. Data will need to be assessed to determine if transforming is acceptable or if reprocessing original survey data or performing new observations is necessary to meet your requirements.

GEOID MODELS: GEOID2022 will replace GEOID18 with NSRS modernization and will be a purely gravimetric geoid model. GEOID2022, which is based on the latest airborne and terrestrial gravity data acquired by the NGS, will be defined to best fit global mean sea level at the epoch of NAPGD2022. At some time in the future when global sea level changes by a threshold level, a new geoid model and geopotential datum will likely need to be released.

STATE PLANE COORDINATE SYSTEM: The current State Plane Coordinate System of 1983 (SPCS 83) will be replaced by SPCS2022 in the Modernized NSRS. States were given the option to have zone "layers" (Figure 6) to better meet the needs of their geospatial communities. Local surveyors and other mapping professionals were often direct contributors to the design of the zones. Figure 7 illustrates the number of zones per state and also highlights special use zones that span jurisdictions.

SUMMARY OF NSRS MODERNIZATION CHANGES: A high-level summary of the changes discussed so far is included in Table 1 below. By no means is this table (or site) intended to be an exhaustive resource - rather, they are intended to provide an overview and resources to further your knowledge of and preparation for NSRS Modernization.

The time to start preparing for NSRS Modernization is now! The NGS has started releasing  Alpha  and  Beta  products, and will continue until modernization is completed. Following is a list of items to help you get started:

1. Check to see if your state has updated its statutes to accommodate NSRS Modernization. We are tracking progress on the map below as a starting point. However, it is also a good idea to check with your  state's geodetic advisor  or  professional surveying association  for more information.
2. If your state has not updated its legislation and is looking for a place to start, the following  document  provides good guidance for preparing updated statutory language and was a collaborative effort between NSPS, AAGS, and NGS. It should be noted that statewide legislation is not the only consideration. There may also be regional, county, and municipal rules and ordinances that need to be updated as well, and your state-focused groups, such as ad hoc task forces and state surveying and mapping organizations may not have the resources to address them. This is a good opportunity for you to get involved at those levels to ensure your geographic area is prepared for the upcoming datum changes.

3. Get to know the new State Plane Coordinate System of 2022 (SPCS2022). The NGS has  published zone information, design status, and example coordinates and distortion values, along with an Alpha NGS Coordinate Conversion and Transformation (NCAT) tool . They have also produced a great  interactive map  shown below to help you explore. Worried about knowing which zone you are working in? Pro tip: Launch the interactive map on your phone or other connected device, tap the location icon, and you will see what zone you are standing in!

4. Talk to your hardware and software vendors. Make sure they are tracking the new datum changes ( more than likely they are - the NGS has done a great job with outreach to this group). Do not forget about small niche specialized software that may not get the attention that nationally distributed software does. These software packages may not be "mainstream,' but they may be crucial to your organization's critical path workflow or are the only software to address local or special datums you use. Figure out their plans for testing and rollout and how that might impact your work. Some are offering beta testing opportunities - a great opportunity to get involved early an ease into the transition of using the modernized NSRS. If your software vendor does not have a concrete plan for addressing the new datums, please contact  NGS  and the group in your  state  working on the new datum implementation and inform them of this software package.

5. Make every effort to understand the "how and why" behind software transformations. Learn how to select the best and most appropriate transformation(s) out of the hundreds available to achieve results appropriate for your needs. DO NOT just pick a transformation based on the name in a pick list.

6. METADATA!! Yes, the dreaded "m" word. It has always been vitally important to the work we do as surveyors and geospatial professionals, and the modernized NSRS only amplifies the need. To ensure the fidelity and usability of your data today and into the future, you should consider capturing, at a minimum, the following attributes:

• acquisition date and time
• reference frames (datums)
• coordinate epochs
• units (e.g. U.S. survey feet, international feet, or meters)
• geoid models applied
• positional accuracy statistics (i.e. 1 sigma, 2 sigma)

7. Some best practices include:

• archiving survey reports
• storing original observation files (e.g. RINEX, processed GNSS vector files, or total station files) in case data needs to be reprocessed or transformed
• documenting any workflows involving coordinate transformations or conversions
• assessing and recording any uncertainty in data so it can be accounted for in future transformations
• storing data versions including geodetic coordinates (latitudes, longitudes, and ellipsoid heights) relative to the NSRS even if deliverables are developed in planar coordinates

8. Geospatial data stewards such as federal, state, regional, county, and municipal agencies should act NOW to:

• Inventory existing data and update and expand current metadata.
• Revise geospatial data acquisition contract templates to specifically include robust metadata.
• Revise geospatial data acquisition contract template deliverables to include the "best practices" above to ensure successful datum transformations or recomputations in the future.
• Identify and rank your data sets' priority for conversion to the new datums based not only on internal needs but also external downstream use.
• Start budgeting for the conversion of your data NOW! Include both the data inventory/prep and the actual conversion.

10. GET INVOLVED!

Many resources have already been provided throughout this guide and more follow:

1.  NGS Blueprint Documents 
2.  NGS Get Prepared 
3.   ¹ Ready, Set, Modernize: ASPRS Takes on Preparing the Geospatial Industry for the Modernized National Spatial Reference System (NSRS) 
4.  Prepare your data for the National Spatial Reference System Modernization of 2022 in the U.S. (Esri) 
5.  NOAA's New Geodetic Datum (xyHt) 
6.  The Geospatial Industry is Getting Ready for the Modernized National Spatial Reference System (Geo Week News) 

This site has been assembled by NSPS and is intended to be a living resource for surveyors and other geospatial professionals as we move towards the adoption of the Modernized NSRS. It can, and likely will, change frequently as more resources and updated information become available- so please do not make this your last visit! Is there something you think would be helpful that we have not included? Please  let us know .

We have done our very best to ensure the information included is current and correct, but changes are occurring rapidly, and we cannot make any guarantees. Where appropriate, we have linked back to the NGS or other authoritative sources to eliminate redundancy and improve reliability.