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The kilometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: km; /ˈkɪləmiːtər/ or /kɪˈlɒmɪtər/) or kilometer (American spelling) is a unit of length in the metric system, equal to one thousand metres (kilo- being the SI prefix for 1000). It is now the measurement unit used officially for expressing distances between geographical places on land in most of the world; notable exceptions are the United States and the road network of the United Kingdom where the statute mile is the official unit used.
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The former follows a pattern in English whereby metric units are pronounced with the stress on the first syllable (as in kilogram, kilojoule and kilohertz) and the pronunciation of the actual base unit does not change irrespective of the prefix (as in centimetre, millimetre, nanometre and so on). It is generally preferred by the British Broadcasting Corporation (BBC) and the Australian Broadcasting Corporation (ABC).
Many scientists and other users, particularly in countries where the metric system is not widely used, use the pronunciation with stress on the second syllable. The latter pronunciation follows the stress pattern used for the names of measuring instruments (such as micrometer, barometer, thermometer, tachometer and speedometer). The contrast is even more obvious in countries using the British rather than American spelling of the word metre.
When Australia introduced the metric system in 1975, the first pronunciation was declared official by the government's Metric Conversion Board.
However, the Australian prime minister at the time, Gough Whitlam, insisted that the second pronunciation was the correct one because of the Greek origins of the two parts of the word.
Equivalence to other units of length
By the 8 May 1790 decree, the Constituent assembly ordered the French Academy of Sciences to develop a new measurement system. In August 1793, the French National Convention decreed the metre as the sole length measurement system in the French Republic. The first name of the kilometre was "Millaire". Although the metre was formally defined in 1799, the myriametre (10000 metres) was preferred to the "kilometre" for everyday use. The term "myriamètre" appeared a number of times in the text of Develey's book Physique d'Emile: ou, Principes de la science de la nature,  (published in 1802), while the term kilometre only appeared in an appendix. French maps published in 1835 had scales showing myriametres and "lieues de Poste" (Postal leagues of about 4288 metres).
In 1935, the International Committee for Weights and Measures (CIPM) officially abolished the prefix "myria-" and with it the "myriametre", leaving the kilometre as the recognised unit of length for measurements of that magnitude.
Some sporting disciplines feature 1000 m (one-kilometre) races in major events (such as the Olympic Games). In some disciplines—although world records are catalogued—one-kilometre events remain a minority.
Kilometre world records (for various sporting disciplines):
|Running (M)||Noah Ngeny||2:11.96||Rieti, Italy||5 Sep 1999||Not an Olympic event|
|Running (F)||Svetlana Masterkova||2:28.98||Brussels||23 Aug 1996||Not an Olympic event|
|Speed Skating(M)||Shani Davis||0:58.92||Salt Lake City||7 Mar 2009|
|Speed Skating(F)||Cindy Klassen||1:13.11||Calgary||25 Mar 2006|
|Cycling(M)||Arnaud Tourant||58.875||La Paz, Bolivia||10 Oct 2001||No official1000 mwoman's record|
Conversion of units, for comparison with other units of length
Orders of magnitude (length)