ZIP Codes are five digits long. The first digit is assigned to a broad geographical area of the United States, ranging from zero in the Northeast to nine in the West. The next two digits pinpoint population concentrations and sectional centers accessible to common transportation networks. The final two digits in the code designate small Post Offices or postal codes in larger zoned cities.
ZIP Codes and ZCTAs (ZIP Code Tabulation Areas) serve different purposes. ZIP Codes are postal codes created by the USPS for mail delivery, and are not correlated to geographical coordinates. ZCTAs provide a way to analyze census data in relation to ZIP Code areas while maintaining geographic consistency and protecting privacy. In addition, there are more ZIP Codes than ZCTAs, because many ZIP Codes for PO Boxes or unique entities don't have corresponding ZCTAs (US Census).
The data shown reflect ZCTAs from the US Census. As of 2025, there are 33,791 ZCTAs (US Census).