University of Wisconsin–Madison

Wisconsin Geospatial News

US Survey Foot to be phased out in 2022

According to a recent notice by the National Geodetic Survey (NGS) the US Survey Foot will be phased out as part of the modernization of the National Spatial Reference System in 2022.

According to the notice, representatives from NGS, the National Institute of Standards and Technology (NIST) and the Department of Commerce’s Office of the General Counsel unanimously decided to phase out the survey foot. “NIST and NGS will issue a Federal Register Notice (FRN) to solicit public comment on the proposed change. A second FRN will formally announce the change, with the details and process of this change based on the comments received.”

An NGS webinar giving the background on this change can be viewed here.

The U.S. survey foot is longer by 2 parts per million than the international foot. Conversions from feet to meters and vice versa must use the appropriate conversion factors to obtain correct results. As stated in the Wisconsin County Reference Systems Handbook (2nd Edition, page 3), “The international foot, based upon a redefinition of the meter in 1959, is equivalent to exactly 0.3048 meters. The US Survey Foot is equivalent to exactly 1200/3937 meters, or 0.30480061 meters when rounded to 8 digits.

Some spatial data users are not aware that two different definitions of the foot exist in the United States. The NGS has long used the meter as its official unit of measurement.

The US Survey Foot is referenced in legislation in at least 40 jurisdictions, according to this NGS map. This includes Wisconsin, where it is referenced in Chapter 236. It is unclear at this time how states will be expected to respond to the change at the federal level. The topic will be discussed by the WSRS2022 Task Force, which is focusing on other aspects of the NGS’s plans for National Spatial Reference System modernization in 2022.

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