I'd long known that the largest 100 or so US cities by population gets down to the roughly 200k population level. Extending that to 200 cities is still above 100k (per Wikipedia, #333, Daly City, CA, is pop. 100,007: https://en.wikipedia.org/wiki/List_of_United_States_cities_b...>). The relationship, as with so much else in scaling circumstances, tends to be linear on a log-log scale.
In China, you'd reach position 106 before finding a city of less than one million in population (the US has only nine such cities).
India, checking just now, has 46 cities with > 1 million population, the 100th ranked (Malegaon) is 471k, and at #300 population remains > 100k (Aurangabad).
Keep in mind that "city" is a highly arbitrary definition, and some of the world's largest cities would be the equivalent of metropolitan areas or even states or provinces elsewhere.
The largest city by area actually has a remarkably small population: Sermersooq, Greenland, with a population of 24,148 and land area of 575,300 km^2 (220,000 mi^2), which is not only larger than the US state of Rhode Island (by a factor of nearly 144 times), but all but two US states: only Texas and Alaska are larger, and the latter only modestly so (by 12%).
Urban geography is a complicated topic, and typically you'll find that comparisons are made on the basis of multiple scales and definitions such as metropolitan statistical areas (MSAs) and built-up land area, as well as population, which tend to smooth out arbitrary distinctions of political boundaries and give stronger weight to total demographic or economic influence.