Ranking the world's cities by ethnic mixing — rewarding places that hold many distinct ethnic groups and where the nation's largest ethnic group is least dominant locally.
No dataset exists to rank every city on Earth for this. City-level ethnicity isn't recorded in any comparable global form, the definition of an "ethnic group" varies by country, and some nations (e.g. France) don't collect ethnic statistics at all.
So these are illustrative estimates for the most relevant cities per region — directionally sound, not precise figures. "Largest national group" uses the biggest single ethnic/ancestral group, with the European-origin majority treated as the national group in settler nations.