[midasuni]

That’s about the density of Kowloon walled city. And ignores the available space in the ocean.

[woobar]

Did they grow any food, produce electricity, or had any manufacturing at all in Kowloon?

[throwaway2037]

To be clear, "Kowloon" is different from "Kowloon Walled City". And, yes, they did have very small manufacturing inside.

I highly recommend that you find a copy of this (in)famous book about it: << City of Darkness>> (https://cityofdarkness.co.uk).