Geocoding and Reverse Geocoding in iOS

While developing the iOS applications developer uses the locations to display on the map in their apps. So they have to understand the process of the geocoding and reverse geocoding. So that they can apply this effectively in their apps. This blog will provide the easy understanding of the Geocoding and Reverse Geocoding.

Geocoding – Geocoding is the process of converting address (New York, NY, USA) into the geographical coordinates(40.7127837,-74.0059413). In the iOS it is provided by the CLGeocoder class of CoreLocation framework.

CLGeocoder *geocoder = [[CLGeocoder alloc]init];

[geocoder geocodeAddressString:addressString

completionHandler:^(NSArray* placemarks, NSError* error)

{

       if ([placemarks count]>0)

      {

             CLPlacemark *clPlace = [placemarks objectAtIndex:0];

             CLLocation *location = clPlace.location;

      }

}];

CLPlacemark provides following properties through which we can get more details of a location.

• name
• addressDictionary
• ISOcountryCode
• country
• postalCode
• administrativeArea //The state or province associated with the placemark
• subAdministrativeArea //Additional administrative area information for the placemark
• locality //city
• subLocality //Additional city-level information for the placemark.
• thoroughfare
• subThoroughfare
• region

Reverse Geocoding - Reverse geocoding is the process of converting geographic coordinates(40.7127837,-74.0059413) into a human-readable address(New York, NY, USA). To get the address information iOS provides CLGeocoder class for above iOS 5 version. For iOS 5 and below iOS provides the MKReverseGeocoder class.

For iOS 5 above

             CLLocation *location = [[CLLocation alloc]initWithLatitude:latCord longitude:longCord];

             CLGeocoder *geocoder = [[CLGeocoder alloc] init];

             [geocoder reverseGeocodeLocation:location completionHandler:

             ^(NSArray* placemarks, NSError* error)

             {

                      if ([placemarks count] > 0)

                      {

                          CLPlacemark *placeMark = [placemarks objectAtIndex:0];

                       }

             }];

Using iOS 5 and below using MKReverseGeocoder class.

MKReverseGeocoder* geocoder = [[MKReverseGeocoder alloc] initWithCoordinate:location.coordinate];

geocoder.delegate = self;

[geocoder start];

- (void)reverseGeocoder:(MKReverseGeocoder*)geocoder didFindPlacemark:(MKPlacemark*)place

{

          NSLog(@"%@",place.addressDictionary);

}

- (void)reverseGeocoder:(MKReverseGeocoder*)geocoder didFailWithError:(NSError*)error {

           NSLog(@"Error occured");

}

Using Google API – We can also reverse geocode using the google api.

           NSString *requestUrl=[NSString             stringWithFormat:@"http://maps.googleapis.com/maps/api/geocode/json?   latlng=%f,%f&sensor=false",latCord,longCord];

requestUrl = [requestUrl stringByReplacingOccurrencesOfString:@" " withString:@"%20"];

NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease];

[request setTimeoutInterval:60];

[request setURL:[NSURL URLWithString:requestUrl]];

[request setHTTPMethod:@"GET"];

[request addValue:@"application/JSON" forHTTPHeaderField:@"Content-Type"];

NSURLResponse* response = nil;

NSError* error = nil;

NSString *responseString = nil;

NSData *result = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];

if (error)

{

      NSLog(@"Error occured");

}else

{

      NSMutableDictionary *dicResult = [NSJSONSerialization

     JSONObjectWithData:result

     options: NSJSONReadingMutableContainers

     error: &error];

      if ([[dicResult objectForKey:@"status"] isEqualToString:@"OK"])

      {

            NSArray *arrayResult = [dicResult objectForKey:@"results"];

            if ([arrayResult count]>0)

           {

                 NSLog(@"%@",[arrayResult objectAtIndex:0]);

           }

       }

}

Here is sample project with all of the code from the above tutorial.