I guess that I could go off, find a map of the US and work out the maximum coordinate space. I could then try and find a source of zipcode polygons somewhere on the web and so determine the precision with which the are marked.

But presumably you already know what you are dealing with?

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^3: Speeding up point-in-polygon -- take two by BrowserUk
in thread Speeding up point-in-polygon -- take two by punkish

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