A kilometer (km) is a unit of length used in the metric system of measurement. It is equal to one thousand meters, which is the base unit of length in the International System of Units (SI). Therefore, 1 kilometer is equal to 1,000 meters, 100,000 centimeters, 1,000,000 millimeters, or 0.621371 miles.
Kilometers are commonly used for measuring longer distances on Earth, such as the length of roads, the distance between cities, and the dimensions of geographical features like rivers, mountains, and coastlines. They are also used in various sports and outdoor activities, such as running, cycling, and hiking, to express distances. Kilometers are a convenient unit of measurement for everyday use in many countries around the world that use the metric 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).