Answer:
It all depend on how you define a metropolitan area. If your definititions are a little bit more loose I'd consider Guangzhou to be the largest city in the world with ~46.7 million people. Guangzhou has become increasingly more accepted as the largest city in the world bu typically the most common answer will be Tokyo.
Explanation:
Also, if you were refering to sheer size and area the largest city would be New York City.
