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).
A "link" is a unit of length that is equivalent to 1/100th of a chain. In the United States customary system of measurement, one link is equal to 7.92 inches or 0.201168 meters. It is primarily used in surveying and land measurement.
Links are often used in conjunction with other surveying units like chains and rods to measure distances on land, especially for large plots or parcels of land. The term "link" is rarely used in everyday conversation or modern applications outside of surveying and related fields. Instead, more common units like feet, yards, or meters are used for measuring length in most contexts.