In the United States surveying system, an "inch" is a unit of length, but it is not significantly different from the standard inch used in everyday measurements. An inch in U.S. surveying is equal to 1/12th of a foot, just like the standard inch. This means that one U.S. survey inch is approximately equal to 0.0833333 feet or about 2.54 centimeters.
The primary distinction in U.S. surveying is the use of the survey foot, which is defined as exactly 12 survey inches. This slight difference in the definition of the foot and inch in U.S. surveying is used for precise land measurements and surveying work, especially when dealing with large areas of land. However, for most everyday purposes, the standard inch and foot are used in the United States and other countries that employ the imperial system.
Earth's polar radius, often denoted as "r," is the distance from the center of the Earth to a point on the Earth's surface near either the North Pole or the South Pole. It represents the Earth's radius when measured from its center to a point along its polar axis. The polar radius is shorter than the equatorial radius because the Earth is slightly flattened at the poles and bulges at the equator due to its rotation.
The approximate value for Earth's polar radius is about 6,357 kilometers (or approximately 3,949 miles). This value may vary slightly depending on the reference ellipsoid used for modeling the Earth's shape, but the given value is a commonly used and accurate approximation for most purposes.
In contrast to the polar radius, Earth's equatorial radius (measured from the center to a point on the equator) is slightly longer, approximately 6,378.1 kilometers (3,963.2 miles).