The US has over 200 zip codes with a population density of 20k/sqmile. While 20k/sqmile isn't an 'emblem of urban density' it does show there are several locat

The US has over 200 zip codes with a population density of 20k/sqmile. While 20k/sqmile isn't an 'emblem of urban density' it does show there are several locations a person that enjoys high density can live in.