U.S. survey foot

When the United States adopted the international yard in 1 July 1959¹, the U.S. Coast and Geodetic Survey, mappers of the nation, objected that converting all their geodetic data to international feet would be a horrendous undertaking (remember, this was pre-computer). They were authorized to continue to use the previous definition of the foot, that of the Mendenhall order (U.S. Coast and Geodetic Survey Bulletin 26, April 5, 1893), one foot = ¹²⁰⁰⁄₃₉₃₇ meter. This former foot was then renamed the U.S. survey foot, = 1.000 002 international feet. It was for use only in land measurements. Abbreviation, “sft”.

By 1986, the mapping service had completed converting the national geodetic grid to international feet. However, that was not the case on the state level, where some surveyors continued to work in U.S. survey feet, instead of international feet.

On 17 October 2019, NIST and other relevant agencies announced plans² to deprecate the U.S. survey foot on 31 December 2022. At the same time, the term “international foot” will be phased out, replaced by “foot”, with the same meaning.

1. 24 FR 5348. Available as a pdf file by searching at federalregister.gov.

2. 84 FR 55562
Invitation for public comment

sources

Any data expressed in feet derived from and published as a result of geodetic surveys within the United States will continue to bear the following relationship as defined in 1893:

1 foot = 1200/3937 meter

The foot unit defined by this equation shall be referred to as the U.S. Survey Foot and it shall continue to be used, for the purpose given herein, until such a time as it becomes desirable and expedient to readjust the basic geodetic survey networks in the United States, after which the ratio of a yard, equal to 0.9144 meter, shall apply.

F.R. Doc. 59-5442; Filed, June 30, 1959; 8:45 a.m.

resources

NIST's Physical Measurement Laboratory (PML) announcement of the intention to deprecate. It includes valuable links to other pages on the topic, including a video, by themselves and other agencies. PML

Link to a 51-minute video from the National Geodetic Survey on the 2022 changeover.

A poster from the National Geodetic Survey explaining the State Plane Coordinate System, in which the elimination of the survey foot figures.

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