1990 Census Profiles for ZIP Code Areas

Limitations

Census geography and United States Postal Service (USPS) geography cannot be linked easily. In practice, ZIP Codes are more accurately represented as an open network of lines [postal delivery routes] interspersed with points [post offices]. Any attempt to create ZIP Code areas requires interpretation and adjustment. The ZIP Code delineations in the Summary Tape File (STF) 3B ZIP Code/Block Equivalency file represent a commercial vendor's interpretation of the relationship of ZIP Codes to 1990 census block numbers. There are no "Post Office Box Only" ZIP Codes included in this file.

ZIP Code boundaries typically follow property lines rather than the center lines of streets. For this reason, they do not coincide with census block boundaries. Data users should be aware of this inherent limitation in the ZIP Code tabulations caused by including whole census blocks in a ZIP Code when only some of the housing units are served by that ZIP Code. Some housing units will not be allocated to their true USPS ZIP Code. Unlike census geographic areas, which change only once in every ten years, the USPS can and does change ZIP Codes at any time.

Source: U.S. Census Bureau

Last modified: February 20, 2001
E-mail: OFM.Forecasting@ofm.wa.gov