kilometry

Kilometry is a unit of length in the metric system equal to 1,000 meters. The standard symbol for the unit is km, and the prefix kilo- denotes a thousand. Kilometry is commonly used in everyday measurement of distance, transportation, and geographic expanses.

In the International System of Units (SI), the meter is the base unit of length, and the kilometer is a derived, widely accepted unit. Therefore, 1 kilometer equals 1,000 meters. Although the kilometer is not an SI base unit, it is routinely employed in science, engineering, and daily life because it conveniently expresses moderate to long distances. The concept of the kilometer originated with the metric system introduced in the late 18th century, specifically defined as a part of a framework based on the Earth's meridian; the meter was later redefined in terms of physical constants, while the kilometer remained 1,000 meters.

Kilometry is used for measuring road distances between cities, travel routes, and geographic scales on maps. It also appears in athletics and fitness contexts, where events are described in kilometers, such as 5 km or 10 km races. For more distant measurements, kilometers are often supplemented or replaced by other units, such as miles or astronomical units, depending on the region and field.

Conversions and examples: 1 km is about 0.621371 miles, and 1,000 km equals 1,000,000 meters. The Earth's circumference is roughly 40,075 km. The Moon lies about 384,400 km from Earth at average distance. Spelling variations exist, with "kilometer" (American English) and "kilometre" (British/Commonwealth English); "kilometry" appears mainly as a plural form in some languages.