Current DateSeptember 19, 2021

US abandons the American foot

In 2023, the measurement system used by American surveyors will be unified with the adoption of the international foot instead of the American foot used in certain States.

All American surveyors will finally be on an equal footing. One type of foot, more precisely: the “international foot”. Not content with using this unit of measure of length in use in the Anglo-Saxon world rather than the metric system, they also use two different versions, according to the state in which they are and for whom they work. To eliminate the resulting confusion, surveyors will soon stop using what is known as the “American foot” and will only use its international version.

The two units are almost identical: the international foot is worth exactly 0.3048 meters, while the American foot is worth 1,200 / 3,937 meters, or 0.3048006… meters (its decimal development is infinite). The ratio between their lengths is 0.999998… But over large distances, this tiny difference accumulates and can end up being a problem. In the United States, buildings are located by specific GPS coordinates, which are usually given in meters. When drawing up cadastres or building plans, surveyors convert these meters into feet. If they use the wrong type of unit, the engineers who will then refer to these maps risk building or looking for infrastructure in the wrong place.

“It’s a bit of a mess,” says Michael Dennis, project manager for the National Geodetic Survey, the federal agency responsible for the United States’ coordinate system. Most engineering projects in the United States have used the international unit since 1959, but topographic surveys – who help map borders and the location of infrastructure – use the unit desired by any organization or state. This means that anyone working in multiple regions of the United States or with different agencies should be very careful about the type of foot used. A recent survey of 530 participants in a National Geodetic Survey seminar, mostly surveyors, found that 62% of them attributed the problems in their work to the confusion between the two feet.

It is common to make miscalculations when trying to interpret the measurements of other colleagues, says Brian Fisher, land surveyor in Arizona. “I’ve seen it dozens if not hundreds of times in my career. Fortunately, he adds, “it’s not a mistake until you build the building.” But Michael Dennis recalls that this happens, citing the case of a building which was built too close to an airstrip, and which had to be shortened by one floor at the last minute to avoid hindering the trajectory of aircraft descent, calculated with a different type of foot.

The abandonment of the American foot in favor of the international foot by the United States was set for December 31, 2022. The public had previously been consulted on this decision: some people expressed their support; Others believe it could cause even more confusion, and some suggest that the United States simply adopts the metric system. “We really want to move to the metric system,” admits Michael Dennis, “but it’s a battle of another magnitude. “