public static function createGeocodingProvider( $provider_code = GeocodingProviders::GOOGLE_MAPS ) {
    if ( GeocodingProviders::GOOGLE_MAPS != $provider_code ) {
      throw new GeocodingException( 'Geocoding provider \'' . $provider_code . '\' not found.' );
    }

    return new \BlueBlazeAssociates\Geocoding\PostalCodes\Providers\GoogleMapsProvider();

    // TODO Create a map between provider keys and implementation class names.
  }