Oh something I totally missed to explain is that Tokyo is not built like most European/American cities, or even most Japanese cities; it's a city of cities so to speak, so the circle is not around a "life center" (it's somewhat around the imperial family castle, but there's no normal people living there). The circle line stops on the important "cities" that conform Tokyo, which are built in somewhat of a circle itself! The big buildings and everything is on the Yamanote line then. And it's fairly big, not what you'd have as a circle line in most EU cities, it takes a bit over 1h to go around in train. A bit like London, but more extreme.
That is how the newer American cities are laid out as well. Look at a map of Los Angeles or Dallas-Fort Worth or any other sprawling American city and you'll find the exact same layout as Tokyo: many small cities that grew into one giant city, with many of them having their own "downtowns"/"CBDs".
