Maybe I'm misunderstanding something, but those population numbers seem very wrong. Last I checked, NYC only had about 8.4 million people and Tokyo only 13.9. Does this include the surrounding suburbs?
The metropolitan area around New York City includes ares in the states of New York, New Jersey, Connecticut, and Pennsylvania. The best I can tell that's what this graphic is basing it's population of NYC on.
Edit: actually I can guarantee is the metropolitan are because Tokyo is the same way. The city has a listed population of 13 million but the metropolitan area is around 40 million, this map shows 37 million.
Yes. This map says "human settlements", not "population counts within city limits". There are various ways to define the borders of an urban settlement, and the numbers represented seem to align with the figures under "urban area" in this list, which is defined within and pulled from this report.
The numbers are close to, but not quite, what Wikipedia has. They’re using 2018 UN estimates, which includes the entire metro area, not just the city proper. I’m assuming OP is using a more recent version of this data, as it’s at least 5 years old at this point.
No clue about Japanese cities, but if you search for an American city's population you'll get the metropolitan population, not the greater city's population. That's how, according to Wikipedia, Sydney has a similar population to LA, despite LA having 10x the population density. If you include the suburbs LA is an order of magnitude larger than Sydney.
Similar with any UK city other than London and a few small ones, it makes it easy to spot mapmakers who've used the metro/borough population based on whether they include Manchester (borough 550k, metro 2.72M), Birmingham (borough 1.15M, metro 2.59M) on their maps... I've also seen some include Liverpool though (looking at you hoi4) when it's smaller than both in all metrics