NSNumber conversion-pair latitude and longitude
NSNumber *a;

for(NSDictionary *item in[res valueForKey:@"snapshot"])
{
a=[item valueForKey:@"lat"];
NSLog(@"%@",a);
b=[item valueForKey:@"lng"];
NSLog(@"%@",b);
}

for(NSDictionary *item in[res valueForKey:@"snapshot"])
{
    NSArray* latitudesList  = [item valueForKey:@"lat"];
    NSArray* longitudesList = [item valueForKey:@"lng"];
    NSInteger idx = 0;
    NSInteger nb = MIN( latitudesList.count , longitudesList.count );
    for(NSInteger idx = 0; idx < nb; ++idx)
    {
      double lat = [[latitudesList  objectAtIndex:idx] doubleValue];
      double lng = [[longitudesList objectAtIndex:idx] doubleValue];
      NSLog(@"Pair #%d = { %f , %f }", idx, lat, lng);
    }
}