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For various reasons the United States and Great Britain adopted the wavelength of the krypton-86 atom as the new standard for the length of the meter in 1959. Prior to this, the meter was based on a platimum-iridium bar made in France in 1897, often referred to as the meter bar.
So, as of 1959, we now have a new length for the meter, but what about the foot? It seems that by treaty, law, or regulation (unknown to the author) the length of the foot is officially tied to the length of the meter. The new shorter meter means a new shorter foot must also be defined. The technocrats were having a field day (along with a few drinks, I believe).
A tale may help make clear what happened to the foot in 1959. Say an old surveyor at USC&GS uses his calibrated yardstick (pun intended) to measure a line exactly 1,000,000 feet in length in 1957. In 1961, the new whiz kid private surveyor with his new calibrated yardstick remeasures the line and finds the line is exactly 1,000,002 feet in length. The whiz kid immediately declares that his yardstick is better, and the USC&GS does not know how to measure anyhow.
The surveyors at the USC&GS probably wanted nothing to do with a change in the foot. Change the length of the foot!!! Who needs the meter anyhow! On top of that, the new whiz kids will say we did not know how to measure. The USC&GS was probably the only agency that published large numbers in feet. A change in the length of the foot would mean millions of numbers would have to be converted and republished.
So, its was decided that the line measured by the USC&GS would remain 1,000,000 feet in length. For everyone else, the same line would be 1,000,002 feet in length. To be sure that it was clear (yeh!) the USC&GS line would be called 1,000,000 U.S. Survey Feet, and everyone else would call the same line 1,000,002 International Feet.
Well, what it really says is that "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 defined in 1893: 1 foot = 1200/3937 meters". Read it for yourself. That is, geodetic distances will be expressed in the U.S Survey Foot. The U.S. now stands on it's own two feet (pun intended).
I guess it goes like this. If you measure how far the home run ball was hit for the record book, you should use the International Foot. If you then plot home plate and the point of impact on a map, then the distance should be expressed in U.S. Survey Feet.
Okay, this ends it, right? Wrong! The politicians have not put in their two cents worth yet. Many states have passed laws stating which foot is to be used with NAD83. One must check their state law to determine which foot (if any. Yes, IF ANY!) is to be used in surveying. Those states that implemented the NGS model law may be supprised to learn that surveyors MUST (by law) use the meter with NAD83. Note that the U. S. Survey Foot should always be used with NAD27.
As of 1988, the states that define NAD83 only in meters are: Alaska, Georgia, Louisiana, Maine, Minnesota, Missouri, Nevada, New Hampshire, Ohio, Rhode Island, South Dakota, Vermont, Virginia, and West Virginia.
I am not sure if the law allows the use of the foot (with NAD83) in the above states. However, I believe that if the foot is used (NAD83 or not), it should be the U. S. Survey Foot. The reasoning being that if no new relationship of the foot and meter is specified by state law, then the federal relationship defined in 1893 applies.
As of 1988, the states that have specified the the use of the International Foot for NAD83 are: Arizona, Michigan, Montana, Oregon, South Carolina, and Utah.
As of 1988, the states that have specified the the use of the U. S. Survey Foot for NAD83 are: California, Connecticut, Indiana, Maryland, North Carolina, and Texas.
It also seems (to the author) that the U. S. Survey Foot should be used (in surveying and mapping) when no law or regulation specifies otherwise. That is, all states not mentioned above should use the U. S. Survey Foot. See also the NGS position.
Surveyors should also note that fundamental survey units, such as rods/polls, chains, statute miles, acres, sections, and townships are defined in terms of the U. S. Survey Foot.
Those of you with the latest yardsticks (called GPS) should be careful. The metric distances are always large, and conversion to the incorrect foot can result is unacceptably large errors and the associated embarrassment.