>If I'm not wrong, SOME ZIP codes can be quite large (since a ZIP code (the 5 digit kind anyway) is actually equal to a postal station). Wouldn't that make the possible error factor pretty high?
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>If a Montana ZIP code is 50 miles by 50 miles and you're calculating the distance to an Alaska ZIP code which is also 50 miles by 50 miles -- how do you decide which distance to use? It COULD be from the farthest Northwest corner of Alaska to the farthest southwest corner of the Montana ZIP.
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>That could be a range of 200 miles, right?
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>>Does anyone have a code snippet for calculating the distance between 2 US zip codes in miles?
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>>David

Yeah, but the Post Office building is still only a small thing. That's what they use (I *believe* so, anyways) for the Lat/Long coordinates.