Waiting for a map click.
The population data comes from
GHSL - Global Human Settlement Layer, specifically, the GHS population grid (R2023) snapshot of 2020 at 1km resolution using Mollweide coordinates. I've filtered out all square kilometres with less than 1000 people so you won't find much outside of cities and towns. The population and metadata of the cities comes from the basic list of
SimpleMaps
Don't take this too seriously (part 1): the population numbers are estimates. They do not come from censuses. Highlighting the highest counts is
also a way to highlight artifacts in the dataset. I've censored some
squares from appearing in the "Top in ..." lists when the estimates look clearly wrong but there are still lots of egregious-looking numbers
Don't take this too seriously (part 2): the cities database has its own issues but it's the best I've got access to. Also, since the metadata it gives you
are distance-based, you'll get some strange results (eg click on lower Manhattan and it'll tell you about the top square kilometres in New Jersey)
Over 96% of the code was written by GPT-5.1-codex-max and GPT-5.2-codex