MKMapView setRegion animated does not show animation

Question

I have a MKMapView with annotation pins. When the view was loaded the nearest pin gets searched and the map will get zoomed so it shows both, the user's location and the nearest pin. I do that with [map setRegion:region animated:YES];. Everything works fine up to here. The same method is also called by tapping on a button which locates the user and then does exactly what I just described.

I also have a search field with which the user can search for map points. When the user taps on one of the search results the map sets the region so the searched pin is in the middle. Now, there's something strange with that. I also set this region animated, at least I do the same command as above. But if the map point is too far away from the current visible part of the map it doesn't show the animation when changing the region. Am I missing something? I've already had a look at Apples docs, they don't mention anything regarding any maximum distance for animations.

I'm looking forward to any help!

Update 1:
Just tested it again in the Simulator. An interesting fact is, that when I search for a MapPoint for the first time and then select a search result it doesn't animate. If I perform another search just after the first one and select a result it does animate. As soon as I tap on the locate button which brings the user back to his location and the closest point it doesn't animate for this setRegion: and the first search after that. But only in the Simulator, on my 4S it does exactly what I've described in the original question above.

Update 2:
In the comments I was asked to provide example coordinates.
So here the coordinates for the first step (searching of the own location and the nearest pin):
My Location: 47.227131 / 8.264251
Nearest pin: 47.251347 / 8.357191
The distance between them is about 22 kilometers. The center of the map is the center between the two pins. The distance from the center to the screen border is 1.5 times the distance between the two points which means about 33 kilometers in this case.
And here a set of coordinates for the second step (searching a map point and selecting it):
Searched pin: 46.790680 / 9.818824
The distance to the screen border is here fixed to 500 meters.

Answer 1

I've tested this issue with a simple demo application on iOS 6 and iOS 7 beta. It turns out that the map view actually not always animates the transition between regions. It depends on how far the regions lay apart. For example a transition from Paris to London is not animated. But if you first zoom out a little bit and then go to London it will be animated.

The documentation says:

animated: Specify YES if you want the map view to animate the transition to the new region or NO if you want the map to center on the specified region immediately.

But as we've seen, we can not rely on the animation. We can only tell the map view that the transition should be animated. MapKit decides whether an animation is appropriate. It tells the delegate if the transition will be animated in -(void)mapView:(MKMapView *)mapView regionWillChangeAnimated:(BOOL)animated.

In order to consistently animate the region change in all cases you will need to animate to a intermediate region first. Let A be the current map region and B the target region. If there is an intersection between the regions you can transition directly. (Transform the MKCoordinateRegion to an MKMapRect and use MKMapRectIntersection to find the intersection). If there is no intersection, calculate a region C that spans both regions (use MKMapRectUnion and MKCoordinateRegionForMapRect). Then first go to to region C and in regionDidChangeAnimated go to region B.

Sample code:

MKCoordinateRegion region = _destinationRegion;    
MKMapRect rect = MKMapRectForCoordinateRegion(_destinationRegion);
MKMapRect intersection = MKMapRectIntersection(rect, _mapView.visibleMapRect);
if (MKMapRectIsNull(intersection)) {
    rect = MKMapRectUnion(rect, _mapView.visibleMapRect);
    region = MKCoordinateRegionForMapRect(rect);
    _intermediateAnimation = YES;
}
[_mapView setRegion:region animated:YES];

---

-(void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated
{
    if (_intermediateAnimation) {
        _intermediateAnimation = NO;
        [_mapView setRegion:_destinationRegion animated:YES];
    }
}

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This helper method is taken from here

MKMapRect MKMapRectForCoordinateRegion(MKCoordinateRegion region)
{
    MKMapPoint a = MKMapPointForCoordinate(CLLocationCoordinate2DMake(
                                                                      region.center.latitude + region.span.latitudeDelta / 2,
                                                                      region.center.longitude - region.span.longitudeDelta / 2));
    MKMapPoint b = MKMapPointForCoordinate(CLLocationCoordinate2DMake(
                                                                      region.center.latitude - region.span.latitudeDelta / 2,
                                                                      region.center.longitude + region.span.longitudeDelta / 2));
    return MKMapRectMake(MIN(a.x,b.x), MIN(a.y,b.y), ABS(a.x-b.x), ABS(a.y-b.y));
}

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The WWDC 2013 session 309 Putting Map Kit in Perspective explains how to do such complex transitions in iOS 7.