If you find a better link for the methodology please let me know.

But simplified it's maybe exactly this from the UN reports glossary:

> Cities: According to the Degree of Urbanization methodology, contiguous geographic areas with a high population density (at least 1,500 people per km2) and a total population of at least 50,000 inhabitants.

https://www.un.org/development/desa/pd/sites/www.un.org.deve...