Editing Gradian (section)

== Relation to the metre {{anchor|Metre}} ==
{{further|History of the metre#Meridional definition}}
{{see also|Arc length#Great circles on Earth|Nautical mile#Similar definitions}}
[[File:Kilometre definition.svg|thumb|An early definition of the [[metre]] was one ten-millionth of the distance from the [[North Pole]] to the [[equator]], measured along a [[meridian (geography)|meridian]] through [[Paris]].]]

In the 18th century, the [[metre]] was defined as the 10-millionth part of a [[quarter meridian]].
Thus, 1&nbsp;gon corresponds to an [[arc length]] along the Earth's surface of approximately 100&nbsp;kilometres; 1&nbsp;centigon to 1&nbsp;kilometre; 10&nbsp;microgons to 1&nbsp;metre.<ref>[http://webdav-noauth.unit-c.fr/files/perso/pbarbier/cours_unit/Elements_de_base_de_la_cartographie.pdf Cartographie – lecture de carte – Partie H Quelques exemples à retenir]. {{webarchive|url=https://web.archive.org/web/20120302111251/http://webdav-noauth.unit-c.fr/files/perso/pbarbier/cours_unit/Elements_de_base_de_la_cartographie.pdf|date=2 March 2012}}.</ref> (The [[metre#History of definition|metre has been redefined]] with increasing precision since then.)