A tale of two feet

[TC Haddad]

Hi folks,

Since the recent share about the upcoming changeover in datums was of interest, I thought some folks might also be interested in another change on the horizon: the dropping of the U.S. Survey foot, scheduled to be finalized sometime this fall.

the high level overview:

https://oceanservice.noaa.gov/geodesy/international-foot.html

For those interested in the history, here's the deep dive video:

https://geodesy.noaa.gov/web/science_edu/webinar_series/videos/fate-of-the-US-survey-foot-after-2022.mp4

Some background quotes:

"An era will soon end. In 1959, the name “U.S. survey foot” was given to an existing definition so that its use could temporarily continue alongside the new “international foot.” After December 31, 2022, only the international foot definition will be used in the United States: 1 foot = 0.3048 meter exactly (but simply called the “foot”). That will stop the simultaneous use of two nearly identical foot versions that differ by only 0.01 foot per mile. "

"Having two feet is great for people, but not so good for standards. Since 1959, two definitions of the foot have been used in the U.S. One is the "international foot", adopted nationwide at that time. The other is the "U.S. survey foot", a renamed perpetuation of the 1893 definition that was intended as temporary. Although the U.S. survey foot is longer by only 2 parts per million (0.01 foot per mile), having both in use at the same time creates real problems with real costs. The result is decades of confusion and chaos in fields where large distances and coordinates are used, such as surveying and mapping. NGS missed an opportunity to fix this problem in 1986, with the change from the NAD 27 to NAD 83 datums. Another opportunity is in 2022 with the modernization of the National Spatial Reference System. "

[Eli Adam]

"large distances and [large] coordinates are used" is really the heart
of the issue, multiplying the small difference by millions.

While it may be nice to finalize dropping the US Survey Foot... it
isn't so simple. All the old data in NAD 27, much of the data in NAD
83, lots of property deeds, and other things are in US Survey Feet.
As long as that information is useful, then the proper metadata and
migration methods are needed to identify and properly migrate the
data. The usefulness of old data is what has kept the US Survey Foot
around for so long already! There are now better tools for migrating
data so maybe this time migrating will work better. Otherwise,
dropping the US Survey Foot is so fun, we can do it again every 15-40
years.

Merry Mapping, Eli


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