Postal routes are not city boundaries
ZIP Codes were designed to support mail processing and delivery, not to reproduce the borders of incorporated cities. Postal routes and delivery areas can cross or divide municipal boundaries.
Population and delivery volume
Large cities, dense neighborhoods and areas with substantial business or apartment delivery needs may require many ZIP Codes. Smaller communities may have fewer codes, but size alone does not determine the exact arrangement.
Preferred city names
USPS address standards may associate a ZIP Code with a preferred city name while allowing certain alternate city names. This is why an address can sometimes use a recognized locality name that differs from the municipality name commonly used in conversation.
What this means for address searches
Do not assume that every address in a city uses the same ZIP Code. Use the street address to identify the correct postal code and verify it with USPS.