Editing List of metro systems (section)

==Legend==
[[File:World Metro systems.svg|thumb|upright=1.35|Countries shown in green have at least one operational metro system. Countries shown in yellow have at least one metro system under construction.]]
; City: Primary city served by the metro system.
; Country: [[List of sovereign states|Sovereign state]] in which the metro system is located.
; Name: The most common English name of the metro system (including a link to the article for that system).
; Year opened: [[File:Metro around the world.png|thumb|Map of all the world's metro systems]]The year the metro system was opened for commercial service at metro standards. In other words, parts of the system may be older, but as parts of a former [[light rail]] or [[commuter rail]] network, so the year that the system obtained metro standards (most notably electrification) is the one listed.
; Year of last expansion: The last time the system length or number of stations in the metro system was expanded.
; Stations: The number of stations in the metro network, with stations connected by [[Interchange station|transfer]] counted as one.
; System length:The [[Network length (transport)|system length]] of a metro network is the sum of the lengths of all routes in the rail network in kilometers or miles. Each route is counted only once, regardless of how many lines pass over it, and regardless of whether it is [[Single track (rail)|single-track]] or [[Double track|multi-track]], [[single carriageway]] or [[dual carriageway]].
; Ridership: The number of unique journeys on the metro system every year. There is a major discrepancy between the ridership figures: some metro systems count [[Transfer (public transit)|transferring]] between lines as multiple journeys, but others do not. Numbers may also be counted via different methods – [[faregate]]s/[[turnstile]]s or [[Light curtain|light barrier]]s at entrances or vehicle doors being the most common but far from the only ones.