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Comment by ry0ohki | Hacker News Reader

My understanding is the whole point of a zipcode is that city and state on a mailer don't matter at all. Doesn't zipcode go to a specific post office?

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I believe to a point it matters. In high density areas there might be a few distribution centers for mail. So the 9 digit zipcode is important. Also, the address lines are still very important. i.e. 1234 mystreet st. apt #2

Depends on if you mean ZIP or ZIP + 4 or ZIP + 4 + delivery point.

ZIP alone will route to a post office, but here are a significant number of areas where city is needed to further disambiguate due to duplicate street addresses in a delivery zone. Now, they obviously try to avoid this, but it still happens.

ZIP+4 would obviate the need for city, state.

ZIP + 4 + delivery point would obviate the need for everything :)

(The need for delivery point is because even a single address may have multiple mailboxes, etc)

Do you have an example of where city would clarify a zip code further? I'd expect large cities to be the case, but New York, NY seems to get everywhere, so maybe it's country roads? And state is certainly unnecessary, are there any zipcodes that cross states?

That is my understanding as well. The person at our local post office recommended putting the township but wasn't aware of exactly why.

My suspicion is that it doesn't matter one bit but I don't know anything about the USPS system.

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