Only cities with 100 000+ inhabitants are displayed. Data was collected using Wikipedia API ; cross-checking with sources shown that the number of cities is ballpark right but no thorough check was done. It is pretty. It is also pretty meaningless.
Details on the
github repo. You won't get all the scripts cuz I stupidly git reset --hard'd them. Data was pasted directly in the HTML as I didn't want to bother with a dev server and that's how I roll.