Kilometers are represented by the letter "km". Kilometer, also known as kilometer, is a unit of length. It is usually used to measure the distance between two places. It is an international standard unit of length. Length unit refers to the basic unit for measuring spatial distance. It is the basic unit formulated by human beings to regulate length.
Length unit refers to the basic unit for measuring spatial distance. It is the basic unit formulated by human beings to regulate length. The international unit is "meter" (symbol "m"), and the common units are millimeter (mm), centimeter (CM), decimeter (DM), kilometer (km), meter (m) and micron（ μ m) , nano (nm), etc. Length units play an important role in various fields.
The length unit "meter" of the international system of units originated in France. In May 1790, a special committee composed of French scientists proposed to take one fourth of the total length of the earth meridian passing through Paris as the length unit - meter, which was approved by the French parliament in 1791.