ZIP Code Tabulation Areas or ZCTAs (pronounced zik-tahs) are a geographic product of the U.S. Census Bureau created to allow mapping, display, and geographic analyses of the United States Postal Service (USPS) Zone Improvement Plan (ZIP) Codes dataset.

ZIP Codes versus ZCTAs

First introduced in 1963, ZIP Code is a trademark of the USPS created to coordinate mail handling and delivery. The USPS assigns ZIP Code ranges to regional post offices, which in turn assign ZIP Codes to delivery routes. Each delivery route is composed of street networks, and/or individual units with high mail volumes, such as high-rise buildings or individual business locations. Within the Census Bureau’s MAF/TIGER System, ZIP Codes are stored as one component of discrete addresses tied to delivery points, including specific housing unit locations. The result is a point-based dataset unsuitable for mapping and many analysis applications.

ZCTAs are generalized areal representations of the geographic extent and distribution of the point-based ZIP Codes built using 2020 Census tabulation blocks. The Census Bureau is restricted by Title 13 from releasing individual housing unit addresses or location information to the public, so point-based ZIP Code data are unsuitable for distribution and publication. However, by aggregating the points and extrapolating them to a polygonal-based unit (census tabulation blocks), disclosure concerns can be addressed and “geographic subtraction*” is prevented.

* “Geographic subtraction” is the comparison of data for overlapping geographic areas to identify the location and characteristics of individual respondents and housing units. This can inadvertently result in data disclosure and is a major concern for geography representing a relatively small area (below county level) or geography with low counts of population or housing units.

Summary of 2020 ZCTA Delineation Methodology

Each assigned 2020 Census tabulation block is part of one distinct 2020 ZCTA.
All 2020 ZCTA Codes are current valid USPS ZIP Codes (as of January 1, 2020).
Not all valid ZIP Codes are represented by a 2020 ZCTA.
For tabulation blocks that contain housing units, the ZCTA represents the ZIP Code associated with the most addresses in that block.
All inhabited areas have 2020 ZCTA coverage.
2020 ZCTA coverage includes zero population blocks that are enclosed within a ZCTA, located along the fringes of a ZCTA, or form a small gap between ZCTAs.
Uninhabited areas (land and water areas) over two square miles are potentially left unassigned from 2020 ZCTA coverage.
2020 ZCTAs may form noncontiguous areas (e.g., islands or enclaves).
A 2020 ZCTA may represent a single institutional or corporate delivery point address.
2020 ZCTAs may represent mixed mail delivery (non-unique), firm or organization-specific (unique), or post office box-only (PO Box) ZIP Codes.
All 2020 ZCTA boundaries are 2020 Census tabulation block boundaries.