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The US National Geodetic Survey (NGS) is implimenting a plan to replace NAD 83 and NAVD 88 through a modernization effort.


NGS’s main page on the subject:


NGS has been very proactive in publishing information on the planned changes, and has had several summits to directly communicate with stakeholders and invite feedback. This year’s is on May 6-7 in Silver Spring, Maryland.


Last year there was a special industry partner summit. We’ve had someone at all of these geospatial summits, and have met many of the NGS personnel who are involved in the effort.


We are also attending or watching the NGS webinars related to this subject to make sure that we’re on top of the situation.


NGS has stated that they will release beta versions of data, transformations, etc. ahead of the 2022 date. So far there hasn’t been anything that Esri can test. We plan to incorporate any new coordinate system definitions (geodetic, projected, and vertical) as they’re released officially. If NGS releases beta versions, we plan to check that we do not see any issues and that they can be used in the software.


We have occasionally pre-empted an official release of transformation grid files or coordinate systems because supposedly the names and other information have been finalized and put the objects into a current software release. Then the names are changed and we end up having to change/delete/add the existing definitions. Because there are a lot of customers using US data, we want to be very careful adding these new coordinate systems and transformations for the 2022 modernization.

A customer had some questions on why Esri has "null" or "bookkeeping" transformations as well as why there are transformations which have the same parameter values, but convert between multiple geographic coordinate systems. Here's what I wrote off the top of my head.



  • WGS84 is actually not accessible to normal consumers because it’s a military system. Yes, GPS reports WGS84, but in a degraded state. RTK/post-processing are actually linking to ITRFxx or local GCS/datum like NAD83 (2011).
  • A lot of data is labeled NAD83 but is really another realization like NAD83 HARN or CORS96 or worse, a mix of several realizations as the dataset has been edited over the years.
  • Similarly, there’s tons of data that’s labeled WGS84 that really isn’t.
  • Some states had one HARN realization, other had 2 or 3. NGS only published conversions between NAD83 (1986) and the first HARN realization, not the later ones.
  • Transformations didn’t exist between HARN, NSRS2007, and 2011 until a few years ago. We’ve put in transformations for GEOCON and GEOCON11 v1.0. There’s a new NGS version in beta that further differentiates between the various HARN realizations, by calling later ones FBN.
  • The NGS CORS website has published some 14 parameter transformations (time-based coordinate frame which has 3 translations, 3 rotations, plus a scale difference plus 7 more parameters that have time components) between ITRFxx or IGSxx (basically equivalent) to NAD83 (realization). Esri has incorporated these as 7 parameter coordinate frames by dropping the time components. That means the transformations occur at the ‘reference epoch.’
  • Knowing there’s a mish-mash of data out there, I’ve put equivalents where I duplicate an ITRF-to-NAD83 with WGS84-to-NAD83 versions. I’ve also added null or “bookkeeping” transformations (where the parameters are zeroes) to get between GeoCRS (geographic coordinate reference systems) where there’s no other transformation or at a certain accuracy level, these can be considered equal.
  • I have not been consistent about it, and have been putting in fewer as time goes on and I learn more about geodesy and as the accuracy has been improving on the more recent realizations.
  • EPSG ( and plan to put in the multiple realizations of WGS84 and Canada’s NAD83 CSRS shortly. We’ll follow, probably for 10.5.1. That’ll make everything even more confusing!

While fine-tuning a technical workshop for next week, my co-presenter and I realized that our comment of "don't forget these knowledge base articles!" (see terminology note below) wasn't very helpful. You used to be able to go to and type in a knowledge base/technical article number like 23025. That would bring up "FAQ: Projection Basics: What the GIS Professional needs to know."


The Support website has been redesigned and that trick no longer works. Below I've included the new links to some of the useful coordinate systems, map projections, and geographic (datum) transformations technical articles.


23025:, FAQ: Projection Basics: What the GIS professional needs to know

17420:, FAQ: Where can more information be found about coordinate systems, map
projections, and datums?

29129:, How To: Identify the
spatial reference, projection, or coordinate system of data

21327:, How To: Select the correct geographic (datum) transformation when
projecting between datums

24893:, How To: Identify an unknown projected coordinate system using ArcMap

How To: Define the projection for CAD data for use in ArcMap


If you have a favorite KB/technical article number, you can also append the number to this partial link:


which will automatically redirect to the new URL.



Terminology note: Originally, they were called knowledge base articles and sometimes referred to as KB articles. A few years ago, the name was changed to technical articles.