US Survey Foot vs International Foot

Did you know that either one you use, you are actually working in meters? In 1893 the United States Congress adopted a definition of the foot as 1 Foot=1200/3937 meters exactly. In 1959 the conversion was changed to 1 Foot=0.3048. This was done to help with international trade. There was however one exception to the use of the new standard, Geodetic Surveying. That is why we have two separate definitions of the foot.You have probably heard by now that on

December 31, 2022, the US Survey Foot was retired by the NOAA and NGS as well as the National Institute of Standards and Technology. What does this mean to us in the surveying community? Do we have to make the change? How should we make the transition on all of the files we use in the projects we are working on? Do we have to change old surveys to show the difference? In short, most of us don’t have to do anything.

In Texas, the use of the US Survey Foot is legislated into the Natural Resources Code under Title 2, Subtitle B, Chapter 21, Subchapter D, Section 21.078. This section specifically spells out that “The plane coordinate values for a point on the earth's surface, to be used in expressing the position or location of the point in the appropriate zone, of either system, shall consist of two distances, expressed in U.S. Survey Feet and decimals of a foot or varas or tenths of a vara when using the Texas Coordinate System of 1927 and expressed in meters and decimals of a meter, in U.S. Survey Feet or decimals of a foot, or in varas or tenths of a vara when using the Texas Coordinate System of 1983.” NATURAL RESOURCES CODE CHAPTER 21. SURVEYS AND FIELD NOTES (texas.gov) 

Taking a wider look, NIST has stated that ““U.S. survey foot” will be permanently maintained in NOAA products and services for legacy applications, for example the computation of SPCS coordinates in States where it was specified for SPCS 83, and for all zones of SPCS 27.” (Federal Register :: Deprecation of the United States (U.S.) Survey Foot) In addition, on the NGS’s FAQ page the following statement is in the eleventh item. “Will deprecation of the U.S. survey foot be delayed? No. The planned effective date of December 31, 2022 will remain the same. This action is coordinated with the National Institute of Science and Technology (NIST) and is independent of the NSRS modernization timeline. An earlier effective date will have no effect on users of the existing NSRS, because NGS will continue to provide the U.S. survey foot in products and services where it is currently supported. It also ensures a timely retirement of the U.S. survey foot, so that it will not be available for any component of the modernized NSRS (including both horizontal and vertical coordinates). See the NIST U.S. survey foot site for more details.” (Frequently Asked Questions - FAQ – New Datums - National Geodetic Survey (noaa.gov)) In addition, Michael Dennis gave a webinar entitled State Plane 2022: Where Things Stand and the Road Ahead. At about the 38:10 mark he starts the discussion about “A tale of two feet” that goes into the depreciation of the Survey foot. At about the the 41:40 mark he talks about the U.S. Survey Foot being used “only for historical and legacy applications.”

In addition to all the above, in personal correspondence with Michael Dennis, the SPCS2022 Project Manager, I was told that “People will continue to use SPCS 83 at least until SPCS2022 is rolled out in 2025. Those states using the sft for SPCS 83 should continue to do so. That means they should continue to use the sft in their equipment and associated software (such as GIS and CAD). Situations may occur after 2022 where an organization uses custom (non-SPCS) coordinate systems. In such cases, my recommendation is to use the sft if it is also being used for SPCS 83. Trying to manage a partial switch (where some things use the ift and others use the sft at the same time) could cause confusion and lead to mistakes. This is in keeping with the “orderly transition” idea stated in the final determination FRN. We understand that the transition may take some time for certain organizations, and that’s OK. The most important part is that it occurs in an orderly fashion. Over time use of the sft will diminish, and we expect that to accelerate after SPCS2022 is released in 2025.”

For more information, please reach out to your NGS Regional Geodetic Advisor or to us at AllTerra Central.