List of urban rail systems in Japan
The list of urban rail systems in Japan lists urban rail transit systems in Japan, organized by , including number of stations, length (km), and average daily and annual ridership volume. Data is shown only for those areas designated as by the Statistics Bureau of the Ministry of Internal Affairs and Communications. Considerations. There are several considerations for the data presented in this list. Station count. Data is broken down at the line level, then rolled up for each specific railway operator. The total station count for each operator is a "unique station" count —an interchange or transfer station between two lines operated by the same company is counted as a single station. As a result, summing together the station counts for all of the lines under a single railway operator will generally yield a value greater than the total station count cited for the operator. Some station pairs are officially considered interchanges by their respective railway operators despite having different names (e.g., Tameike-Sannō and Kokkai-gijidō-mae on the Tokyo Metro and Tenjin and Tenjin-Minami on the Fukuoka City Subway). As such stations have different names, however, they are counted as  separate stations in this list. Length. In a similar fashion to the station count, length is counted as route kilometers, but only considers "unique" segments. The following considerations are relevant for the lengths referenced in the tables. Intra-company considerations. Generally, multiple-track sections classified under the same line name and without operational segregation into separate lines are only counted once, not twice. Examples include the quadruple-track sections of the Keihan Main Line and Tōbu Isesaki Line, which are only counted once because fast (i.e., limited-stop) and slow (i.e., local or all-stop) services are branded together as  a single line, not separately as distinct lines. Other cases include double junctions where a double-track branch line ties into a double-track main line, permitting interlining of the branch line with the main line. Examples include Keiō Sagamihara Line trains that continue past Chōfu Station onto the Keiō Line. In this situation, the trackage of the Keiō Sagamihara Line is counted as only the section between Chōfu and Hashimoto Station, while the double-track section east of Chōfu is counted under the Keiō Line, following traditional conventions for railway line nomenclature in Japan. Likewise, double-track segments shared  by lines under the same operator are only counted once. Examples include the Yamanote Freight Line between Ikebukuro and Ōsaki, a segment shared by the Saikyō Line and Shōnan-Shinjuku Line. In this situation, the trackage is counted only once, under the Saikyō Line. Similarly, tabulations for the larger tram systems with a high degree of interlining, such as Hiroshima Electric Railway, also consider only unique segments, and sections where multiple routes overlap are only counted once. However, if there is some reasonable segregation of operations or distinction between lines, the trackage is counted more than once. Examples include the  various quadruple-track sections of East Japan Railway Company (JR East) that provide segregated local and rapid services (e.g., Chūō Rapid Line vs. Chūō-Sōbu Line). Here, the route-kilometers are counted twice, once under the Chūō Rapid Line and again under the local Chūō-Sōbu Line. Other situations include quadruple-track sections at the confluence of two distinct double-track lines, such as the Ōsaka Uehommachi – Fuse quadruple-track section of the Kintetsu network in central Ōsaka, officially designated as part of the Osaka Line but actually two lines (the Osaka Line and Nara Line) sharing a single right -of-way west of Fuse. A similar situation applies for many JR East lines—the Yamanote Line and Keihin-Tōhoku Line officially use tracks classified as part of the Tōkaidō Main Line and Tōhoku Main Line, but that are fully segregated from the tracks used by the respective services operating under the names "Tōkaidō Line" and "Utsunomiya Line" / "Takasaki Line". Cross-company considerations. As a general rule, trackage used by one company but owned by another company as part of a trackage rights or (often translated as through-service) agreement is not counted under the first company. For example, trackage  on the Toei Asakusa Line is not counted under Keikyu Corporation, Keisei Electric Railway, or the Hokusō Railway, despite the fact that all three operate their trains on the Asakusa Line. However, this list makes some exceptions to this rule, the most notable being the Keisei-Takasago – Inba-Nihon-Idai section of the Keisei Narita Airport Line, which is shared with trains operated by Hokusō Railway but owned partially by Hokusō Railway (Keisei-Takasago – Komuro) and Chiba New Town Railway (Komuro – Inba-Nihon-Idai). This shared trackage is counted once under Hokusō Railway and again under Keisei Electric Railway. Similar  exceptions include trackage owned by third-sector railways that do not own any of their own rolling stock and instead contract out train operations to through-servicing operators. Notable examples include the double-track approach into Narita Airport, which is owned by the third-sector Narita Airport Rapid Railway. All trains on this railway, however, are operated by either JR East or Keisei Electric Railway, with each operator getting dedicated usage of one of the two tracks into the Airport. In this situation, the JR East single-track section is counted in the JR total, while the Keisei single-track  section is counted in the Keisei total. Ridership. Both average daily and annual ridership are included, because only average daily ridership or annual ridership (not both) is available for some operators. In cases where data for only one of the two is available, care has been taken to not extrapolate the passenger volume to obtain the other, as there is a potential margin of error when attempting to derive average daily ridership from annual ridership (which is usually rounded to the nearest thousand passengers) and natural disasters or other unforeseen situations may force some operators to shut down for extended  periods of time, as happened with the Sendai Subway in the days following the 2011 Tōhoku earthquake and tsunami. Categories. For readability and ease of comparison across metropolitan areas, systems within each metropolitan area are broken down into the following categories: