The United States Postal Service groups one or more ZIP codes into what’s referred to as a “USPS Preferred City Name”. The SmartCharts team runs ZIP codes against the USPS Preferred City Name database in order to map every ZIP code to a city. Once we had every ZIP associated with the applicable Preferred City Name, we then ran all listing activity for applicable ZIPs, which were then stored in the City rollups. This methodology was the ideal way to get to a standardized list of cities