Why does the zips database only include one city per zip?

Our US Zip Code Database only includes a single city for each zip code under the city field.  This is primary "city" as listed by the United State Postal Service.  This is typically a city, but it could be a neighborhood.  If you want to get a mapping of all cities that overlap the zip code, you'll need our US Cities Database.  It lists all zip codes that overlap a city in the zips field.  You can query the zips field to get all cities that overlap.