[thelist] Zip/Postal Code Radius

[Carl J Meyer]

Rob,

On Thu, 2002-12-19 at 11:34, Rob Smith wrote:
> This is something I've always been curious about. How do Zip/Postal Code
> finders work where you enter your zip and it brings you the closest
> something sorted by distance? Do you have to have a listing of all known zip
> codes, distances to and fro or is there a website/formula that will
> calculate this for you?

AFAIK in order to actually calculate distances you need software that
will convert zip codes to latitude/longitude numbers.  That software is
available from the USPS for a hefty pricetag, I think they call it Tiger
something.  Otherwise you're limited to just finding things in "similar"
zip codes (ie you can do a decent job finding "somewhat close" addresses
by just using the first three digits of the zip, but that's pretty
inexact.  And there are of course those people who live near a border
between zip codes with different third digits, and it won't work well
for them.  Eventually someone is bound to complain that your finder
didn't find something that's 'practically just across the street').

HTH
Carl