Get latitude/longitude from address

Here's a similar solution for obtaining the latitude and longitude from Google. Note: This example uses the SBJson library, which you can find on github:

+ (CLLocationCoordinate2D) geoCodeUsingAddress: (NSString *) address
{
    CLLocationCoordinate2D myLocation; 

// -- modified from the stackoverflow page - we use the SBJson parser instead of the string scanner --

        NSString       *esc_addr = [address stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding];
        NSString            *req = [NSString stringWithFormat: @"http://maps.google.com/maps/api/geocode/json?sensor=false&address=%@", esc_addr];
    NSDictionary *googleResponse = [[NSString stringWithContentsOfURL: [NSURL URLWithString: req] encoding: NSUTF8StringEncoding error: NULL] JSONValue];

    NSDictionary    *resultsDict = [googleResponse valueForKey:  @"results"];   // get the results dictionary
    NSDictionary   *geometryDict = [   resultsDict valueForKey: @"geometry"];   // geometry dictionary within the  results dictionary
    NSDictionary   *locationDict = [  geometryDict valueForKey: @"location"];   // location dictionary within the geometry dictionary

// -- you should be able to strip the latitude & longitude from google's location information (while understanding what the json parser returns) --

    DLog (@"-- returning latitude & longitude from google --");

    NSArray *latArray = [locationDict valueForKey: @"lat"]; NSString *latString = [latArray lastObject];     // (one element) array entries provided by the json parser
    NSArray *lngArray = [locationDict valueForKey: @"lng"]; NSString *lngString = [lngArray lastObject];     // (one element) array entries provided by the json parser

     myLocation.latitude = [latString doubleValue];     // the json parser uses NSArrays which don't support "doubleValue"
    myLocation.longitude = [lngString doubleValue];

    return myLocation;
}

Update version, using iOS JSON:

- (CLLocationCoordinate2D)getLocation:(NSString *)address {

    CLLocationCoordinate2D center;
    NSString *esc_addr =  [address stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    NSString *req = [NSString stringWithFormat:@"http://maps.google.com/maps/api/geocode/json?sensor=false&address=%@", esc_addr];
    NSData *responseData = [[NSData alloc] initWithContentsOfURL:
                        [NSURL URLWithString:req]];    NSError *error;
    NSMutableDictionary *responseDictionary = [NSJSONSerialization
                                               JSONObjectWithData:responseData
                                               options:nil
                                               error:&error];
    if( error )
    {
        NSLog(@"%@", [error localizedDescription]);
        center.latitude = 0;
        center.longitude = 0;
        return center;
    }
    else {
        NSArray *results = (NSArray *) responseDictionary[@"results"];
        NSDictionary *firstItem = (NSDictionary *) [results objectAtIndex:0];
        NSDictionary *geometry = (NSDictionary *) [firstItem objectForKey:@"geometry"];
        NSDictionary *location = (NSDictionary *) [geometry objectForKey:@"location"];
        NSNumber *lat = (NSNumber *) [location objectForKey:@"lat"];
        NSNumber *lng = (NSNumber *) [location objectForKey:@"lng"];

        center.latitude = [lat doubleValue];
        center.longitude = [lng doubleValue];
        return center;
    }
}

Here's an updated, more compact, version of unforgiven's code, which uses the latest v3 API:

- (CLLocationCoordinate2D) geoCodeUsingAddress:(NSString *)address
{
    double latitude = 0, longitude = 0;
    NSString *esc_addr =  [address stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    NSString *req = [NSString stringWithFormat:@"http://maps.google.com/maps/api/geocode/json?sensor=false&address=%@", esc_addr];
    NSString *result = [NSString stringWithContentsOfURL:[NSURL URLWithString:req] encoding:NSUTF8StringEncoding error:NULL];
    if (result) {
        NSScanner *scanner = [NSScanner scannerWithString:result];
        if ([scanner scanUpToString:@"\"lat\" :" intoString:nil] && [scanner scanString:@"\"lat\" :" intoString:nil]) {
            [scanner scanDouble:&latitude];
            if ([scanner scanUpToString:@"\"lng\" :" intoString:nil] && [scanner scanString:@"\"lng\" :" intoString:nil]) {
                [scanner scanDouble:&longitude];
            }
        }
    }
    CLLocationCoordinate2D center;
    center.latitude = latitude;
    center.longitude = longitude;
    return center;
}

It makes the assumption that the coordinates for "location" come first, e.g. before those for "viewport", because it just takes the first coords it finds under the "lng" and "lat" keys. Feel free to use a proper JSON scanner (e.g. SBJSON) if you are worried about this simple scanning technique used here.

You can use Google Geocoding for this. It is as simple as getting data through HTTP and parsing it (it can return JSON KML, XML, CSV).