The Worlds Biggest Urban Area
The most populous metropolitan area in the world is the Greater Tokyo Area in Japan. When the city of Tokyo is counted together with the dense ring of surrounding cities and prefectures that form one continuous urban region, the total population reaches roughly 37 million people - more than the entire population of many countries.
Why Count the Metropolitan Area
The reason geographers talk about the metropolitan area rather than just the city is that modern cities spread far beyond their official borders. Around Tokyo, neighbouring cities such as Yokohama merge into one vast, connected urban landscape. Counted this way, the Greater Tokyo Area is the clear leader, well ahead of other giant urban regions.
From Fishing Village to Megacity
Tokyos rise is remarkable. It began as a small settlement called Edo and grew, over centuries, into one of the largest cities on the planet by the 1700s. After becoming Japans capital, it continued to expand into the sprawling megacity of today. It is the political, economic, and cultural heart of Japan, home to a huge share of the countrys population.
Source
This article was written using information from Wikipedia.