I don't want to spam this, but I spent too much time writing it to explain this particular case: https://skaldmaps.com/blog/2026/07/zip-codes-are-a-bad-spati...

tl;dr: USPS cares about delivery routes and that's what ZIP codes help with. These happen to make up, more or less, areas. This is close enough an abstraction for many use cases (which is why they are ubiquitous), but pretty horrible once you get into the details.