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Comment by bdn_ | Hacker News Reader

ZIP codes are such interesting identifiers. Their intended use was for facilitating more efficient mail sorting, they were not for providing any sort of human-friendly location data. Yet we still end up using them in so many parts of our lives for identity verification, navigation, population statistics, ...

They remind me of Social Security numbers in a way, where an identifier created for one narrow use (internal Social Security use only) ended up becoming a de facto standard (national identification number) due to the absense of a suitable alternative.

If you'd like to go further down the ZIP code rabbit hole, a few interesting codes to research are `00501`, `48222`, and `12345`. :)

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I find it interesting that we use them to represent areas while they were only intended to represent routes...

And this relates to why there are some ZIP codes that are in multiple states.

Physical routes tend to end in contiguous areas. It's rather difficult to teleport a mail delivery truck.

Is there really no ZIP code that is non-contiguous? I think it might depend on the visualization provided by services, but it looks like on Google Maps, searching for "92014" seems to generate borders around two areas that look like there is no contact between them.

Zip codes are trees, each digit narrows down the area. The final area can be non-contiguous, but 92014 is entirely contained within 9201, that's within 920, etc. up to 9, which is the US west coast area.

ZIP codes are the route a mail truck takes to deliver mail. That mail truck begins and ends it's route at a specific Post Office. The +4 portion of the ZIP code denotes where along the route something is such that mail can be sorted in the order it will be encountered along the route.

So a ZIP code is an area. A ZIP code is often used incorrectly to apply other demographic information such as race or income, those are generalizations and not necessarily 100% accurate.

The route represented by a ZIP code may enclose an area but the ZIP code itself is not an area. It is a set of delivery points.

Another interesting one is `10022-7463` which is commonly communicated as "10022-SHOE" because of how the letters are represented on a U.S. telephone keypad. This is the floor the houses the shoe department of a store, Saks Fifth Avenue.

10048

The classic 90210

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