PRC cities are not particularly dense. Population densities in cities within a country tend to follow zipfs law, which would predict BJ and SH to be 3-4x larger than it currently is. Many economists and urban planners was suggesting PRC should densify tier1 about 10 years ago. But hukou anbd industrial policy seems to be designed to limit megacity sizes to redirect popuation towards growing 3rd, 4th+ tier cities into their own economic hubs. IMO trying to avoid SKR/JP where everyone rushes to a few economically viable regions.