Ladies and Gentlemen, welcome to #TrainTwitter
Today we'll take a look at JR commuter lines--this is the famous Yamanote Line in Tokyopic.twitter.com/yg99ss793w
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The Chuo-Sobu Line runs east-west from Mitaka to Chiba, crossing the Yamanote Line at Shinjuku and Akihabarapic.twitter.com/H47pFnccP7
The Chuo Rapid Line starts at Tokyo Station, parallels the Chuo-Sobu to Mitaka, then continues to Hachioji, Takao, and Otsukipic.twitter.com/pFwBnzhYdl
In the northeast, the Joban Rapid Line runs from Ueno to Toride and Naritapic.twitter.com/oMbnt7sqEr
The Saikyo Line runs from Osaki to Kawagoe, paralleling the western part of the Yamanote Line. Thru service under Tokyo Bay to Shin-Kibapic.twitter.com/QYjlvGJoYq
The Keiyo Line begins deep under Tokyo Station, then hugs the coastline to Soga before branching to either Kimitsu or Katsuurapic.twitter.com/UY5pt1bn9L
The Musashino Line, a vast loop through suburban Tokyo from Fuchu to Funabashi via Urawa, uses older equipment--many thru service optionspic.twitter.com/aBDU16nNc9
The Nambu Line follows the Tama River from Kawasaki up to Tachikawa--the latest line to receive e233 rolling stock!pic.twitter.com/UiB5Rhonws
My beloved Yokohama Line runs from Hachioji to Ofuna via Machida, my old city, and Yokohama.pic.twitter.com/fjWONbk1yc
The two lines that cross in Machida, JR's Yokohama Line and the Odakyu Line 
pic.twitter.com/2pLO598ZmU
From Yokohama to Ofuna, the Yokohama and Keihin-Tohoku Lines share track; this is referred to as the Negishi Linepic.twitter.com/XkyZ4syfKf
The Yokosuka-Sobu Rapid Line starts in Kurihama, passes under Tokyo Station, then branches out to many destinations in Chiba Prefecture...pic.twitter.com/Eiutan2KjA
...specifically Kashima Jingu, Narita Airport, Naruto, Kazusa Ichinomiya, and Kimitsu
Finally, the big three! The Tokaido Line, Utsunomiya/Takasaki Line, and Shonan-Shinjuku Line all use the same rolling stock and colorspic.twitter.com/uwY1Soij69
These lines wrap around downtown Tokyo, connecting far-flung satellite cities as shown by this map...pic.twitter.com/jcWgDtadpE
Until the Ueno-Tokyo viaduct was built, the Tokaido Line terminated at Tokyo, and the Utsunomiya/Takasaki Line at Ueno...
...so that only the Shonan-Shinjuku Line could offer thru service. Fortunately, this is no longer the case!
This has not been an exhaustive listing--other lines in the area include the Ome Line, Itsukaishi Line, Sagami Line, Tsurumi Line...
...and many more, all operated by JR East. However, I wanted to focus today's thread on the most important lines.
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