Guangzhou is usually reported as larger than Shenzhen.
A specific issue with the population of Chinese cities, though, is that the administrative 'city' division in China can be quite larger than what might be expected in the West.
a lot these are pretty bad representations of real population, even in the US.
ex: Jacksonville is listed as the largest city in the southeast, and strictly speaking, this is true because it's a fairly dense population area. But it's a pretty misleading statement to say that it's the largest city.
Jacksonville's metro population is only about 1.5 million.
Atlanta is in the same box and Atlanta's metro population is nearly 4 times larger (5.9 million), Nashville also beats Jacksonville (1.9 million)
I came to make the same comment. I was surprised to see that "technically" Jacksonville is nearly 2x larger than Atlanta but digging deeper it just seems about city borders. Jacksonville is pretty large and not that dense. Atlanta is pretty small and fairly dense. When you look at the metropolitan areas Atlanta is nearly 4x larger than Jacksonville metro area and that really just includes the area covered by MARTA so it is all pretty much "Atlanta".
And they both go to show that statements/calculations about things like urban density are heavily influenced by historically and culturally determined political boundaries and definitions. Even look at the US Census Bureau 80% urban metric that a lot of people like to quote. Lots of small towns with farmlands and orchards (like where I live) are "urban" by this particular definition. And they are "urban" relative to truly rural Wyoming. But they're not urban in the sense of having any of the attributes of a dense city center.
There must be a way to come up with an (almost) universally applicable metric of city-ness, regardless of the adminstrative boundaries, that can be applied to situations like this map. Something like, the area in which the population density is above a certain threshold, and the population that lives in that area.
FiveThirtyEight has done some work in that area for purposes of splitting urban/rural from a political perspective. The article also mentions a couple other examples of something similar.
Although it's often even messier than that. Look at the density of Manhattan vs. NYC as a whole. Or core Paris vs. Paris as a whole. Much less the many American cities with fairly dense but small downtowns but that sprawl far into the distance.
A specific issue with the population of Chinese cities, though, is that the administrative 'city' division in China can be quite larger than what might be expected in the West.