Today I learned that ZIP Codes do not strictly represent geographic areas but rather “address groups or delivery routes”.
> Despite the geographic derivation of most ZIP Codes, the codes themselves do not represent geographic regions; in general, they correspond to address groups or delivery routes. As a consequence, ZIP Code “areas” can overlap, be subsets of each other, or be artificial constructs with no geographic area (such as 095 for mail to the Navy, which is not geographically fixed). In similar fashion, in areas without regular postal routes (rural route areas) or no mail delivery (undeveloped areas), ZIP Codes are not assigned or are based on sparse delivery routes, and hence the boundary between ZIP Code areas is undefined. […]
ZIP Codes are therefore not that reliable when doing geospatial analysis of data:
> Even though there are different place associations that probably mean more to you as an individual, such as a neighborhood, street, or the block you live on, the zip code is, in many organizations, the geographic unit of choice. It is used to make major decisions for marketing, opening or closing stores, providing services, and making decisions that can have a massive financial impact.
> The problem is that zip codes are not a good representation of real human behavior, and when used in data analysis, often mask real, underlying insights, and may ultimately lead to bad outcomes. To understand why this is, we first need to understand a little more about the zip code itself.

(Via The Bear with Its Own ZIP Code by Jason Kottke)

I ran into this a decade ago, plus or minus a few years, when trying to come up with a good mechanism for imprecisely denoting the general location of network equipment. One idea had been to use the ZIP code or outside-of-the-US postal equivalent in device naming or SNMP strings. I determined ZIP codes and their analog are useful in postal delivery but are not good for asset and information management. I think there was a substantial cost for a database with every possible Earthly postal code, which would have been a massive overkill for the need.