JR in Tokyo

Yamanote Line is a main line of JR (Japan Railways) in Tokyo.
It makes a big circle and has major stations like Shinjuku, Ikebukuro, Akihabara, Tokyo, Shinagawa, Shibuya etc.

It has 31 stations and takes about one hours to make a circle.
So, it'll take about 30 minutes to go to the station on the other side of the circle.

Keihin Tohoku Line goes side by side with Yamanote Line on East side of the circle.
From Tabata through Shinagawa, Keihin Tohoku Line skips stations during daytime.

Chuo Line goes from South to North. (Tokyo - Shinjuku etc.)
It has Rapid train which skips stations and Local train which stops all stations.

Shinjuku has the most passengers in Japan.
Average is about 750,000 passengers a day.

The second is Ikebukuro with 550,000 passengers followed by Tokyo with 420,000 passengers.