: The first three digits of a U.S. ZIP code, known as a ZIP3 , identify the Sectional Center Facility (SCF) —the central mail processing hub for a region. Organizations use ZIP3 data archives for high-level market analysis and logistics planning.

Archives containing this type of geographic or postal information typically include: 3RD SUPERVISORIAL DISTRICT ZIP CODE LISTING*

: In some postal systems, such as NZ Post , "RD" stands for Rural Delivery . A file labeled rd3 might contain data specific to the 3rd rural delivery route in a particular region. Common Data Formats

: Local governments, such as the Los Angeles County 3rd Supervisorial District , maintain specific lists of ZIP codes within their boundaries for voting, service delivery, and planning. An archive like rd3.zip may contain spreadsheets or GIS boundary files for such a district.