Question

I have an android app that finds your current location but I need to figure out which zip codes are within, say, 20 miles of the current location. What would be the best way to find this information? Is there a public API or web service? I can give latitude/longitude or zip code as input.

Answer 1

I would start by using the Haversine formula. Use the result you get from this to find the zipcode relative to that radius.

import com.google.android.maps.GeoPoint;  

public class DistanceCalculator {  

   private double Radius;  

   // R = earth's radius (mean radius = 6,371km)  
   // Constructor  
   DistanceCalculator(double R) {  
      Radius = R;  
   }  

   public double CalculationByDistance(GeoPoint StartP, GeoPoint EndP) {  
      double lat1 = StartP.getLatitudeE6()/1E6;  
      double lat2 = EndP.getLatitudeE6()/1E6;  
      double lon1 = StartP.getLongitudeE6()/1E6;  
      double lon2 = EndP.getLongitudeE6()/1E6;  
      double dLat = Math.toRadians(lat2-lat1);  
      double dLon = Math.toRadians(lon2-lon1);  
      double a = Math.sin(dLat/2) * Math.sin(dLat/2) +  
         Math.cos(Math.toRadians(lat1)) * Math.cos(Math.toRadians(lat2)) *  
         Math.sin(dLon/2) * Math.sin(dLon/2);  
      double c = 2 * Math.asin(Math.sqrt(a));  
      return Radius * c;  
   }  
}