Get map view region based on all annotation pin for screen fit size zoom.

Region+Annotations+MapView.mm

-(MKCoordinateRegion) regionForAnnotations:(NSMutableArray *)annotations
{
    double minLat=90.0f, maxLat=-90.0f;
    double minLon=180.0f, maxLon=-180.0f;
    
    for (id<MKAnnotation> mka in annotations) {
        if ( mka.coordinate.latitude  < minLat ) minLat = mka.coordinate.latitude;
        if ( mka.coordinate.latitude  > maxLat ) maxLat = mka.coordinate.latitude;
        if ( mka.coordinate.longitude < minLon ) minLon = mka.coordinate.longitude;
        if ( mka.coordinate.longitude > maxLon ) maxLon = mka.coordinate.longitude;
    }
    
    CLLocationCoordinate2D center = CLLocationCoordinate2DMake((minLat+maxLat)/2.0, (minLon+maxLon)/2.0);
    MKCoordinateSpan span = MKCoordinateSpanMake((maxLat-minLat)+0.5f, (maxLon-minLon)+0.5f);
    MKCoordinateRegion region = MKCoordinateRegionMake (center, span);
    
    return region;
}