This is an alphabetical list of cities worldwide that have a metro rail system . Metros are rapid transit systems and are sometimes referred to as a subway or underground.
This page uses the definition found in the metro article, under which a metro system:
Minato Mirai Line (http://www.mm21railway.co.jp/www/index.html)
Notes
Note 1: There are four systems in KCR. East Rail shares track with inter-city and freight trains on most but not all of its tracks. West Rail was designed as a commuter railway like East Rail, but contains only within-Hong Kong service currently, and is operating as a metro. The third one is the Light Rail system. A fourth one, the Ma On Shan Rail, is a branch of East Rail containing only local passenger service.
The East Rail was opened in 1910 as part of a raillink to Canton (now Guangzhou), the Kowloon-Canton Railway, with some local service. It was electrified in the early 1980s, and over 95% of services on its track are now metro-like passenger service within Hong Kong's territories.
The Madrid metro is the large metrosystem serving Madrid, the capital of Spain.
It is one of the largest metrosystems in the world, which is especially remarkable considering Madrid's population of approximately four million.
The metro is operated by its own company, under the Department of Public Works, City Planning, and Transportation of the autonomous community of Madrid.