liviing in large cities have the best medical care due to few reasons:
1) rich people tend to live in large cities, and they can afford the best doctors. Hence best doctors tend to be in large cities
2) good univerisities tend to make good doctors too, which in again happen to be in large citites
3) 1) is on a per capita basis. Also due to the large population in large cities, it is unsurprising best doctors tend to be in large cities as they have more patients
