In the United States surveying system, a "link" is a unit of length that is equal to 1/100th of a chain. Each link is approximately 7.92 inches long or about 0.201168 meters. This unit is primarily used in surveying and land measurement in the United States.
Surveyors often use a chain, which is comprised of 100 links, to measure distances in land surveys. The use of links and chains allows for precise measurements of land parcels, boundaries, and property lines.
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).