Well, Postal Code is a geographical region but it's not one aligned with legal boundaries.

These are all real scenarios I've lived/have family who has lived:

- Town A contains a region called "Village B" with no distinct government structure. However, Village B has its own post office, so a subsection of Town A has a separate ZIP Code and is delivered mail by this second post office.

- Town C contains two disjoint sub-regions (unincorporated villages) called "Village D" and "Village E." Both have post offices and both have their own ZIP Codes. Some addresses in Village D are delivered mail by the post office in Village E—not the one in Village D.

- Town F has its own post office, but a street in town F receives mail delivered by the post office in Town G.

The practical impact of these is twofold:

- Mail is written to addresses not matching the municipal governmental structure of your town/city. - Mapping apps that rely on USPS data to provided addresses (which is generally good, because it means mail will go to the right place) will show the wrong legal town names for the structure.