I have heard so much about Tokyo in the past but i never knew this
So Tokyo is the largest agglomeration of the world, because it is not a single city but several cities. What is meant by "the center of Tokyo" is the 23 districts circled by the Yamanote line. Originally they were independent cities that were merged together over time.
This story is really informative as i now understand most of the things I have heard about Tokyo in the past. Thanks for sharing @vcelier, credit to @japon.