Berlin has 3,944 inhabitants per km2. If not even that city reaches the standard, I think the criteria must be flawed. My city is the third largest in Mexico and it has less than 3500/km2.

Or maybe we need an article about ghost countries.

I guess the standards necessarily are different for a city of skyscrapers

Pudong was definitely in that range before it was developed. Chinese densities are completely different from the rest of the word. No one calls a 3500/km2 area a ghost city of it is built for 3500/km2, but if it’s built for 10k/km2 with lots of 30 story apartment blocks, there are a lot of empty units and you can play football in the overbuilt 8 lane streets.

Berlin has forests within its borders.

So does Mumbai (the Sanjay Gandhi National Park) and it still supports a density of 73,000 people/sq km.

What? Wikipedia has Mumbai at just 21k/sqkm, and even that seems to be megacity (urban) density, not its metro density, which is only 4,700/sqkm. I assume the national park is in the latter and not the former.

https://en.wikipedia.org/wiki/Mumbai

https://en.m.wikipedia.org/wiki/Mumbai_Metropolitan_Region