I asked myself what were the respective size of Berlin, Paris and Tokyo inside of the Ringbahn (S41/S42), the Yamanote and the boulevards des Maréchaux (that are between 33 et 37km long), so I know which one is the longest to visit by feet.This image was created using the pifomètre method (rough approximation). I have made screen-shots on Openstreetmap.org, and I have resized them to the same scale.

By selecting the inner zones of each city, I get the following values:

• Paris: 646 000 pixels
• Berlin: 638 000 pixels
• Tokyo: 463 000 pixels

Obviously, the comparison is futile. Tokyo is much wider than the sole Yamanote inner side and is much more dense than Berlin.