US Postal Service ZIP Code boundaries. For more information, click here.ZIP is an acronym for Zone Improvement Plan.Legal vs. Postal CitiesMany users confuse the name the Post Office delivers main to (e.g. Van Nuys, Hollywood) as a legal city (in this case Los Angeles), when they are a postal city. The County contains 88 legal cities, and over 400 postal names that are tied to the ZIP Codes. To support usability and geocoding, we have attached the first 3 postal cities to each address, based upon its ZIP Code.