From: Dan Diebolt <dandiebolt@...>
Date: 2005-12-14T02:59:42+09:00
Subject: Re: US Zipcode API for Ruby?

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There is a 40,000+ zip code database in CivicSpace labs that has lat and long by zip code:
   
  http://civicspacelabs.org/home/developers/download
   
  http://civicspacelabs.org/releases/zipcodes/zipcodes-csv-10-Aug-2004.zip
   
  Distance between two points (lat, long) is calculated using the Haversine formula:
   
    dlon = lon2 - lon1
  dlat = lat2 - lat1
  a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2
  c = 2 * atan2(sqrt(a), sqrt(1-a)) 
  d = R * c

  See the following link or google for more: 
   
  http://mathforum.org/library/drmath/view/51879.html

			
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