Zipcode Radius Search

Want to find all zipcodes and corresponding distances within a certain mile/kilometer radius from another zipcode or point? This problems require latitude and longitude coordinates to solve. Geocoding the address gives you latitude/longitude coordinates from an address. Both Yahoo and Google offer free geocoding services. I wrote a post about geocoding with a code example for both Google and Yahoo geocode services.

First you will need a database of all zipcodes and their corresponding latitude and longitude coordinates. If you are reading this post, you probably don't have this so let me help you out. Download Zipcode Database for a zip file of both an SQL data dump and CSV format. Here is the basic table structure I use in my example code:

CREATE TABLE `zipcodes` (
`zipcode` varchar(5) NOT NULL DEFAULT '',
`city` varchar(100) NOT NULL DEFAULT '',
`state` char(2) NOT NULL DEFAULT '',
`latitude` varchar(20) NOT NULL DEFAULT '',
`longitude` varchar(20) NOT NULL DEFAULT '',
KEY `zipcode` (`zipcode`),
KEY `state` (`state`)
)

So once you have the database you want to find all zipcodes within a certain mile radius of a central point. If the central point is another zipcode, simply query the database for the latitude and longitude coordinates of that zipcode. Then the code is as follows:

// ITITIAL POINT

$coords = array('latitude' => "32.8", 'longitude' => "-117.17");

//RADIUS

$radius = 30;

// SQL FOR KILOMETERS

$sql = "SELECT zipcode, ( 6371 * acos( cos( radians( {$coords['latitude']} ) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians( {$coords['longitude']} ) ) + sin( radians( {$coords['latitude']} ) ) * sin( radians( latitude ) ) ) ) AS distance FROM zipcodes HAVING distance <= {$radius} ORDER BY distance";

// SQL FOR MILES

$sql = "SELECT zipcode, ( 3959 * acos( cos( radians( {$coords['latitude']} ) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians( {$coords['longitude']} ) ) + sin( radians( {$coords['latitude']} ) ) * sin( radians( latitude ) ) ) ) AS distance FROM zipcodes HAVING distance <= {$radius} ORDER BY distance";

// OUTPUT THE ZIPCODES AND DISTANCES

$query = mysql_query($sql);

while($row = mysql_fetch_assoc($query)){

echo "{$row['zipcode']} ({$row['distance']})<br>\n";