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Technical Article   HowTo:  Determine which NAD_1983_To_WGS_1984 transformation to use

Article ID: 24159
Software:  ArcGIS - ArcEditor 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcInfo 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcView 9.2, 9.3, 9.3.1, 10
Platforms: N/A

Summary

When originally defined, North American Datum 1983 (NAD 1983) and World Geodetic System 1984 (WGS 1984) were equivalent. In order to minimize coordinate changes, NAD 1983 is tied to the North American and Pacific (for Hawaii, etc.) tectonic plates. WGS 1984 is tied to the International Terrestrial Reference System (ITRF), which is independent of the tectonic plates. Over time, the two coordinate systems became increasingly different.

Instructions provided help in determining the correct datum transformation to use when transforming data between the NAD 1983 and the WGS 1984 datums.

Procedure

  • NAD_1983_To_WGS_1984_1
    Published accuracy from the European Petroleum Survey Group (EPSG) is 2 meters. This transformation applies to the entire North American continent. Accuracy of the transformation varies, with greater accuracy at southern latitudes and less accuracy at more northern latitudes with a maximum offset of 2 meters.

    This transformation uses the Geocentric Translation method, with the transformation's parameters (dx, dy, and dz) all equal to zero. This transformation treats the NAD 1983 and WGS 1984 datums as though they are equivalent.

    NAD_1983_To_WGS_1984_2
    Calculated by the U. S. Defense Mapping Agency (DMA), now known as the National Geospatial Intelligence Agency (NGA), for the Aleutian islands. Accuracy is listed by EPSG at +/-8 m.
     Effective with version 9.3 of ArcGIS Desktop, this transformation method should no longer be used. Use transformation NAD_1983_To_WGS_1984_5 for Alaska and the Aleutian Islands instead.


    NAD_1983_To_WGS_1984_3
    Calculated by the NGA for Hawai'i. Accuracy is listed by EPSG at +/-4 m.

    NAD_1983_To_WGS_1984_4
    Formerly applied within the 48 contiguous states, but is superseded by _5.
     This transformation method should no longer be used.


    NAD_1983_To_WGS_1984_5
    Transformation parameters calculated by the U. S. National Geodetic Survey (NGS) using CORS stations, and ties WGS 1984 to ITRF96. This transformation method should be used for the 48 contiguous states and for the state of Alaska, as well, effective with version 9.3 of ArcGIS Desktop.

    NAD_1983_To_WGS_1984_6, _7, and _8
    Canadian NTv2 transformations, for the Quebec, Saskatchewan and Alberta provinces, respectively.
     The NTv2 transformation grids for each of these transformations must be installed on the computer, or the transformation will not be performed on the data. For additional information, refer to Knowledge Base articles 18317 and 35152 in the Related Information section below.


  • One of the most important considerations in selecting a geographic transformation is consistency: using the same transformation each time to transform between these two Geographic Coordinate Systems (datums). When using the Project Tool, the transformation method is recorded in the metadata.
  • The EPSG database can be downloaded from the similarly titled link in the Related Information section below. This database is a free download and is updated frequently. This database includes information on the source of datum transformation parameters and in many cases, includes the accuracy of the transformation from the transformation source.
     ArcGIS Desktop version 9.2 uses information from version 6.10.2 of the database. Version 9.3 uses information from version 6.13. ArcGIS Desktop version 10.0 uses information from version 7.4.

  • The difference between the GRS 1980 spheroid, the basis for the NAD 1983 datum, and the WGS 1984 spheroid is 0.0001 meters in the length of the semi-minor axis - the distance between the geodetic center of the earth and the North Pole. The semi-minor axis for GRS 1980 is 6356752.3141 meters. This axis for WGS 1984 is 6356752.3142 meters, while the semi-major axis both spheroids measures 6378137 meters.

Related Information


Created: 12/31/2002
Last Modified: 6/1/2011

Article Rating: (2)
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Comments

By TrevorGonskaNAU - 08/21/2013 3:50 PM

Great article! It helped a lot!

I dont understand why others are having difficulty understanding and applying the information in this article. I found it very helpful.

Rating:

By Anonymous - 04/25/2011 9:50 AM

I followed the article’s instructions, but experienced another problem. I’ve provided details below.

I found this article in the HowTo section. It is *NOT* a How To. In order for it to be a How To, it needs to be re-written in user-friendly English. For example: "To determine which transformation method to use, first you need to determine which part of the globe you will be mapping. If you are mapping in the continental USA, then the most appropriate transformation is NAD_1983_To_WGS_1984_1. However, if you are mapping Hawaii, use... or if you are mapping Alaska use..." Something like that!

Rating:

By Anonymous - 06/13/2007 12:03 PM

The article needs to be updated.

the article does not give any info for when transformations 2,3,6,7 & 8 might be most relevant.

By Anonymous - 06/13/2007 11:56 AM

The article needs to be updated.

the article says the information shown is only relevant up to arcgis v9.1, but does not tell users of v9.2 what to do or direct them where else they need to read if they have a similar question (like I do).

By Anonymous - 12/08/2006 10:34 AM

The article needs to be updated.

Hi there, this article is great, and served me well in 9.1. But in 9.2 it looks like there are now 8 different transformations to choose from. Which one to choose? Also, I'd love to hear about any other documentation available about projections/coordinate systems changes between 9.1 and 9.2 - especially since I'm teaching a class on it in February! thanks! Amanda Henley ahenley@email.unc.edu