The Haversine formula to calculate distances:

• #C example http://blogs.techrepublic.com.com/programming-and-development/?p=634
• A lot of talking … http://mathforum.org/library/drmath/view/51879.html
• http://www.ruby-forum.com/topic/48815

Get ZIP codes in range

• http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/174783
• http://forums.devshed.com/php-development-5/how-can-i-search-my-database-using-an-array-like-534211.html?p=2052453
• http://www.hotscripts.com/listing/zip-code-range-and-distance-calculation-class/

Ruby Gems

• http://github.com/collectiveidea/graticule/tree/master
• http://github.com/andre/geokit-gem/tree/master
• http://github.com/andre/geokit-rails/tree/master

Finding visitors via their IP address

• http://www.hostip.info/

Use Google Maps to display the results check this post here

The next is taken from: http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/174783

Below are my zipcode notes. None of this originates from me, so I
really can't help much if you should have questions. Caveat emptor.
But there's probably a gem or two hidden somewhere in all the cruft.

-------------------------------------------------------------------

You can get zip code data and a MySQL schema here:

http://www.sanisoft.com/ziploc/

There is some PHP code there for searching that can easily be ported to Ruby:

class ZipCode < ActiveRecord::Base

         def search(radius = 30)
                 ZipCode.find_by_sql("SELECT * FROM zip_codes WHERE
(POW((69.1*(lon-#{self.lon})*cos(#{self.lat}/57.3)),2)+
  POW((69.1*(lat-#{self.lat})),2))<(#{radius}*#{radius})")
         end
end

OR

This can be done through the use of free Geocoding websites and a little math.

One such site is GeoCoder.us (Web based, or API for a fee ..I beleive), where you can input the addresses (not just zip codes... which is what you asked for, but its close.  "1 main street,
ZIP CODE" is usually a fair assumption.

http://geocoder.us/

Once you have both longitude/latitude coordinates for the addresses, you can then calculate the distance between the two. Here are two links which explain how:

http://jan.ucc.nau.edu/~cvm/latlongdist.html
http://www.mathforum.com/library/drmath/view/51711.html

As for Rails/Ruby solutions.. I don't know of any off hand, but there is a Perl interface to Geocoder.us which may be easily ported or referenced to help you on your way:

http://search.cpan.org/~sderle/Geo-Coder-US-1.00/US.pm

OR

http://maps.huge.info/

OR

http://www.zipcodedownload.com/

OR

http://www.zipinfo.com

OR

http://geocoder.us/
[http://www.hyperionreactor.net/node/87]

------------------------------------------------------------------------------------------
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

 >> Excellent!  The only thing remaining is an efficient algorithm for a search
 >> for all zipcodes within a given radius.

Using Ruby and SQLite3:

   pabs@halcyon:~/proj/zip> ./import.rb zipcode.{csv,db}
   pabs@halcyon:~/proj/zip> ./find.rb zipcode.db 22003 3
   "city","state","zip","distance (mi)"
   "Annandale","VA","22003","0.0"
   "Springfield","VA","22161","1.62363604423677"
   "Springfield","VA","22151","1.87190097838136"
   "Falls Church","VA","22042","2.97362028549975"

Here's the code for each piece (also available at the URL
http://pablotron.org/files/zipfind.tar.gz):

   ---- import.rb ----
   #!/usr/bin/env ruby

   # load libraries
   require 'rubygems' rescue nil
   require 'sqlite3'

   # constants
   SCAN_RE = /"(d{5})","([^"]+)","(..)","([d.-]+)","([d.-]+)","([d-]+)","(d)"/
   SQL = "INSERT INTO zips(zip, city, state, lat, long, timezone, dst)
                 VALUES (?, ?, ?, ?, ?, ?, ?)"
   TABLE_SCHEMA = "CREATE TABLE zips (
     id        INTEGER     NOT NULL PRIMARY KEY,

     zip       VARCHAR(5)  NOT NULL,
     city      TEXT        NOT NULL,
     state     VARCHAR(2)  NOT NULL,
     lat       FLOAT       NOT NULL,
     long      FLOAT       NOT NULL,
     timezone  INTEGER     NOT NULL,
     dst       BOOLEAN     NOT NULL
   );"

   # handle command-line arguments
   unless ARGV.size == 2
     $stderr.puts "Usage: #$0 <csv> <db>"
     exit -1
   end
   csv_path, db_path = ARGV

   # load database, create zip table and prepared statement
   db = SQLite3::Database.new(db_path)
   db.query(TABLE_SCHEMA)
   st = db.prepare(SQL)

   # parse CSV and add each line to the database
   db.transaction {
     File.read(csv_path).scan(SCAN_RE).each { |row| st.execute(*row) }
   }
   ----------

   ---- find.rb ----
   #!/usr/bin/env ruby

   require 'rubygems'
   require 'sqlite3'

   MI_R = 1.15

   # grab base zip code
   unless ARGV.size > 1
     $stderr.puts "Usage: #$0 <db> <zipcode> [radius]"
     exit -1
   end
   db_path, src_zip, radius = ARGV
   radius = (radius || 50).to_i

   # open database
   db = SQLite3::Database.new(db_path)

   # get lat/long for specified zip code
   sql = "SELECT lat, long FROM zips WHERE zip = ?"
   src_lat, src_long = db.get_first_row(sql, src_zip).map { |v| v.to_f }

   unless src_lat && src_long
     $stderr.puts "Unknown zip code '#{src_zip}'"
     exit -1
   end

   # calculate min/max lat/long
   ret, range = [], radius / 69.0

   # get all codes within given rectangle
   sql = "SELECT lat, long, city, state, zip
            FROM zips
           WHERE lat > ? AND lat < ?
             AND long > ? AND long < ?"
   args = [src_lat - range, src_lat + range,
           src_long - range, src_long + range]

   db.prepare(sql).execute(*args).each do |row|
     # get row values, convert lat/long to floats
     dst_lat, dst_long, dst_zip, dst_city, dist_st  = row
     dst_lat, dst_long = dst_lat.to_f, dst_long.to_f

     # calculate distance between zip codes.  if dst_zip is within the
     # specified radius, then add it to the list of results
     d = Math.sqrt((dst_lat - src_lat) ** 2 + (dst_long - src_long) ** 2)
     ret << [dst_zip, dst_city, dist_st, d * 69.0] if d <= range
   end

   # sort results by distance
   ret = ret.sort { |a, b| a[-1] <=> b[-1] }

   # print out results as a CSV
   puts '"city","state","zip","distance (mi)"',
        ret.map { |row| '"' << row.join('","') << '"' }
   ----

 >> I suppose one technique might be to first narrow the databse search within a
 >> given a given square latitude/longitude range and then filter those results
 >> by testing that they are within the given circle radius

That's all the code above does.  There's some room for optimization
there; for example, you could create a region field, then calculate list
of regions that intersect with the search radius.  If you index on the
region field, then the query becomes essentially an index lookup instead
of a lat/long comparison (you still have to do the second distance
calculation, of course).

Landon wrote:

> Hello,
>
> I'm still very new to Ruby, however am growing to like the language more 
> and more as I use it.
>
> Presently, I'm looking for some classes(I'm used to java, sorry, not 
> sure what you'd call them in Ruby) that can measure geographic distances 
> based on information like zip, city, state, etc.
>
> An example of the sort of the functionality I'm looking for would be the 
> "find locations withing X miles of zip code 01234" searches you can do 
> with google maps or mapquest.
>