ZCTAs are approximate area representations of U.S. Postal Service (USPS) 5-digit ZIP Code service areas that the Census Bureau creates using census blocks to present statistical data from censuses and surveys. The Census Bureau defines ZCTAs by allocating each block that contains addresses to a single ZIP Code tabulation area, usually to the ZCTA that reflects the most frequently occurring ZIP Code for the addresses within that block. Blocks that do not contain addresses but that are completely surrounded by a single ZIP Code tabulation area (enclaves) are assigned to the surrounding ZCTA; those surrounded by multiple ZCTAs will be added to a single ZCTA based on the longest shared border. The Census Bureau identifies ZCTAs using a 5-character code that represents the most frequently occurring USPS ZIP Code within that ZCTA. This code may contain leading zeros. Users should not use ZCTAs to identify the official USPS ZIP Code for mail delivery. The USPS makes periodic changes to ZIP Codes to support more efficient mail delivery. ZIP Codes that cover primarily nonresidential or post office box addresses may not have a corresponding ZCTA because the delineation process uses primarily residential addresses, resulting in a bias towards ZIP Codes used for city-style mail delivery. For more information on ZCTAs, visit: <https://www.census.gov/programs-surveys/geography/guidance/geo-areas/zctas.html> See Appendix O-3 5-digit ZIP Code Tabulation Area (ZCTA) National Record Layout.

The TIGER/Line Files are to tl_2020_us_zcta520.shp was downloaded from https://www.census.gov/cgi-bin/geo/shapefiles/index.php.

Features in San Diego County boundary were projected to NAD 83 State Plane.