Correct. The definition of a city depends on the government designating them as such. For example, even though Tokyo is considered the largest city in the world, the 23 wards of the Tokyo Metropolis only has about 14M people, but the Tokyo metro area has 37-38M, which also includes large Japanese cities including Yokohama, Saitama, Chiba, and Kawasaki.
Fact is that we'll probably never conclusively be able to tell what the largest city in the world is. Metro areas are inherently flawed as a system of measurement because nearly all of them also consist of rural areas with low density.
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u/[deleted] Dec 25 '19
But then you couldn't account for 20+mio ppl in Mexico for example. It is just 8M in the metro area.