Given coordinates, how do I get all the Zip Codes within a 10 mile radius?

Question

I have a location (latitude & longitude). How can I get a list of zipcodes that are either partially or fully within the 10 mile radius of my location?

The solution

Answer 1

Firstly, you'll need a database of all zipcodes and their corresponding latitudes and longitudes. In Australia, there are only a few thousand of these (and the information is easily available), however I assume it's probably a more difficult task in the US.

Secondly, given you know where you are, and you know the radius you are looking for, you can look up all zipcodes that fall within that radius. Something simple written in PHP would be as follows: (apologies it's not in C#)

function distanceFromTo($latitude1,$longitude1,$latitude2,$longitude2,$km){
  $latitude1  = deg2rad($latitude1);
  $longitude1 = deg2rad($longitude1);
  $latitude2  = deg2rad($latitude2);
  $longitude2 = deg2rad($longitude2);
  $delta_latitude  = $latitude2  - $latitude1;
  $delta_longitude = $longitude2 - $longitude1;
  $temp = pow(sin($delta_latitude/2.0),2) + cos($latitude1) * cos($latitude2) * pow(sin($delta_longitude/2.0),2);
  $earth_radius = 3956;
  $distance = $earth_radius * 2 * atan2(sqrt($temp),sqrt(1-$temp));
  if ($km)
    $distance = $distance * 1.609344;
  return $distance;
}