The United States stands on two different feet, one a little longer than the other.
But according to a National Geodetic Survey announcement in the Federal Register: not to worry.The feet in this case are the kind made of inches, and what some saw as a possible problem arose from the fact that different states have laws setting different official lengths for the foot. There are two feet in use and they differ by about 22 millionths of an inch.
"For all practical purposes this isn't going to mean a whole lot to most people," said James E. Stem of the survey, official keeper of the country's surveying and mapping standards. "But it does matter to surveyors and mappers."
The difference amounts to almost a foot per 100 miles. Depending on which foot surveyors used, state boundaries, for example, might shift two or three feet.
The discrepancy dates to 1893 when the United States declared the official foot to be 1200-3937ths of a meter (the same as saying a meter is 39.37 inches and that a foot is 12 of those inches). The meter was taken as the basis because most countries, even then, were on the metric system. This is officially called the U.S. Survey Foot.
Then, in 1959, the survey proposed a new definition based on setting the inch equal to exactly 2.54 centimeters. This was an attempt to correct discrepancies in conversion standards used internationally. This foot, about 22 millionths of an inch shorter than the U.S. Survey Foot, was named the International Foot.
In a 1959 Federal Register notice, the survey said the country could keep the Survey Foot until the agency put out new mapping standards, called a geodetic survey network or a datum.
This is a system of map coordinates in which an exact latitude and longitude are assigned to each of 500,000 bronze markers, or monuments, already placed around the country. It is from the Xs on these monuments that surveyors and mappers reckon distances.
Once the new datum was in use, the 1959 notice said, the International Foot would have to be adopted. Each state sets the standard for its jurisdiction but the notice, having the force of law, would have required a uniform national foot.
The new mapping standards were published in 1986 but since then, Stem said, only five states have adopted the International Foot.
In most of the country, the Survey Foot is still enforced in legal definitions and used in land surveys, tax maps and other applications. Faced with a less-than-enthusiastic reception for the International Foot, the survey is withdrawing the part of the 1959 notice that would have mandated its adoption. "We're no longer going to insist on adoption of the International Foot," Stem said. "Actually, as long as you specify which system you're using, there's no real problem."