These things keep surprising me ... (I'd have put money on Mexico City having a larger population than NYC; I thought Toronto had more population than Montreal, but I've still have guessed Montreal much higher than 19th, overall ).
I would like to know how they calculated the population of New York City as 23+ million. I understand that they are including some of the surrounding areas, but if you add the population of NYC (8.5 million) + Westchester (0.9 million) + New Jersey (8.8 million) + Connecticut (3.6 million) it only adds up to 21.8 million, and I would estimate that less than half of New Jersey and Connecticut is anywhere near NYC.
The numbers look like Metropolitan Statistical Areas (MSA)...at least for the US. That's defined by the census bureau. No one has ever come up with a good definition of this in my opinion--at least not any that's been widely adopted.
Yep, you are right. The map shows that they include all of New Jersey, Connecticut, Westchester and Long Island. There is a lot of farm land and forest that they include in New York CITY.
Back in the day they called it the "tri-state area". Seems about right that it would be the most populated metro area in the US.
Largest Cities In Europe https://www.worldatlas.com/articles/largest-cities-in-europe-by-population.html