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The small difference between the survey foot and the international foot would not be detectable on a survey of a small parcel, but becomes significant for mapping, or when the state plane coordinate system (SPCS) is used in the US, because the origin of the system may be hundreds of thousands of feet (hundreds of miles) from the point of interest.
The US survey foot is defined so that 1 metre is exactly 39.37 inches, making the international foot of 0.3048 metres exactly two parts per million shorter. This is a difference of just over 3.2 mm, or a little more than one-eighth of an inch per mile.
For most applications, the difference between the two definitions is insignificant – one international foot is exactly 0.999 998 of a US survey foot, for a difference of about 1 ⁄ 8 in (3 mm) per mile – but it affects the definition of the State Plane Coordinate Systems (SPCSs), which can stretch over hundreds of miles. [14]
In the United States, surveyors and civil engineers use units of feet wherein a survey foot breaks down into 10ths and 100ths. Many deed descriptions containing distances are often expressed using these units (125.25 ft). On the subject of accuracy, surveyors are often held to a standard of one one-hundredth of a foot; about 1/8 inch.
The Beginning Point of the U.S. Public Land Survey is at a point on the Ohio-Pennsylvania border between East Liverpool, Ohio, and Ohioville, Pennsylvania, on private property. A National Historic Landmark marker commemorating the site lies on the side of a state highway, exactly 1,112 feet (339 m) to the north of the point. [4]
Since the difference between the US survey acre and international acre (0.016 square metres, 160 square centimetres or 24.8 square inches), is only about a quarter of the size of an A4 sheet or US letter, it is usually not important which one is being discussed. Areas are seldom measured with sufficient accuracy for the different definitions to ...
The American football field, which has a playing area 100 yards (91.4 m) long by 160 feet (48.8 m) wide. This is often used by the American public media for the sizes of large buildings or parks. It is used both as a unit of length (100 yd or 91.4 m, the length of the playing field excluding goal areas) and as a unit of area (57,600 sq ft or ...
The United States retained the 1 / 39.37 -metre definition for surveying, producing a 2 millionth part difference between standard and US survey inches. [47] This is approximately 1 / 8 inch per mile; 12.7 kilometres is exactly 500,000 standard inches and exactly 499,999 survey inches.