Why don't they do IQ tests on a per-city basis? It seems a little unfair to compare cities like Hong Kong and Singapore to countries like Russia or the US. Obviously a city will have better oppurtunities for education and advancement than some backwater village. The people in the cities will tend to be smarter because smarter people will emigrate there and the better oppurtunities. Surely this is a better measure of how smart an individual nation is, by ranking the avg IQ of their 10 cities and comparing that to other nations?

I've heard that certain european cities average similar to singapore and Hong kong but I struggle to find much research on the IQ in cities. Anyone able to find anything?