gistfile1.m

- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated
{
    if (!self.manuallyChangingMap) {
        BOOL updateRegion = NO;
        MKCoordinateRegion restrictedRegion = [self restrictedRegion];
        if ((mapView.region.span.latitudeDelta > restrictedRegion.span.latitudeDelta * 4) || (mapView.region.span.longitudeDelta > restrictedRegion.span.longitudeDelta * 4) ) {
            updateRegion = YES;
        }
        
        if (fabs(mapView.region.center.latitude - restrictedRegion.center.latitude) > restrictedRegion.span.latitudeDelta) {
            updateRegion = YES;
        }
        
        if (fabs(mapView.region.center.longitude - restrictedRegion.center.longitude) > restrictedRegion.span.longitudeDelta) {
            updateRegion = YES;
        }
        if (updateRegion) {
            self.manuallyChangingMap = YES;
            [mapView setRegion:region animated:YES];
            self.manuallyChangingMap = NO;
        }
    }
}