What's the best way to zoom out and fit all annotations in MapKit

Question

Quick background of what I have going on. UIMapView loads and shows a single annotation (Never more than one). On the menu bar, there is a Locate Me button, on tap the userLocation is found and displayed as a second annotation. I then I have MapView zoom out to fit both those annotations in range but I am unable to find a suitable way of doing so. Depending on where the first annotation is placed in relation to the user location, sometimes it doesn't zoom out enough.

For example, if the annotation is North West of the User, it zooms out fine. But if the annotation is South East of the User, it only zooms out enough that they are just getting cut off and you have to manually zoom out a bit more. Here's the code I am using, variation of some others I have found on SO.

        CLLocation *whereIAm = mapView.userLocation.location;

        float lat = whereIAm.coordinate.latitude;
        float lon = whereIAm.coordinate.longitude;


        CLLocationCoordinate2D southWest = {[currentLatitude floatValue], [currentLongitude floatValue]};
        CLLocationCoordinate2D northEast = southWest;

        southWest.latitude = MIN(southWest.latitude, lat);
        southWest.longitude = MIN(southWest.longitude, lon);

        northEast.latitude = MAX(northEast.latitude, lat);
        northEast.longitude = MAX(northEast.longitude, lon);

        CLLocation *locSouthWest = [[CLLocation alloc] initWithLatitude:southWest.latitude longitude:southWest.longitude];
        CLLocation *locNorthEast = [[CLLocation alloc] initWithLatitude:northEast.latitude longitude:northEast.longitude];

        CLLocationDistance meters = [locSouthWest distanceFromLocation:locNorthEast];

        MKCoordinateRegion region;
        region.center.latitude = (southWest.latitude + northEast.latitude) / 2.0;
        region.center.longitude = (southWest.longitude + northEast.longitude) / 2.0;
        region.span.latitudeDelta = meters / 111319.5
        region.span.longitudeDelta = 7.0;

        MKCoordinateRegion savedRegion = [mapView regionThatFits:region];
        [mapView setRegion:savedRegion animated:YES];

        [locSouthWest release];
        [locNorthEast release];

Is there a better way built into MapKit to just zoom out so that both annotations have, lets say half an inch between them at the outer frame? I don't really care if the user has to zoom in after, I just want it to zoom out properly.

Answer 1

-(void)zoomToFitMapAnnotations:(MKMapView*)mapView
{
    if([mapView.annotations count] == 0)
        return;

    CLLocationCoordinate2D topLeftCoord;
    topLeftCoord.latitude = -90;
    topLeftCoord.longitude = 180;

    CLLocationCoordinate2D bottomRightCoord;
    bottomRightCoord.latitude = 90;
    bottomRightCoord.longitude = -180;

    for(MapAnnotation* annotation in mapView.annotations)
    {
        topLeftCoord.longitude = fmin(topLeftCoord.longitude, annotation.coordinate.longitude);
        topLeftCoord.latitude = fmax(topLeftCoord.latitude, annotation.coordinate.latitude);

        bottomRightCoord.longitude = fmax(bottomRightCoord.longitude, annotation.coordinate.longitude);
        bottomRightCoord.latitude = fmin(bottomRightCoord.latitude, annotation.coordinate.latitude);
    }

    MKCoordinateRegion region;
    region.center.latitude = topLeftCoord.latitude - (topLeftCoord.latitude - bottomRightCoord.latitude) * 0.5;
    region.center.longitude = topLeftCoord.longitude + (bottomRightCoord.longitude - topLeftCoord.longitude) * 0.5;
    region.span.latitudeDelta = fabs(topLeftCoord.latitude - bottomRightCoord.latitude) * 1.1; // Add a little extra space on the sides
    region.span.longitudeDelta = fabs(bottomRightCoord.longitude - topLeftCoord.longitude) * 1.1; // Add a little extra space on the sides

    region = [mapView regionThatFits:region];
    [mapView setRegion:region animated:YES];
}

Taken from: http://codisllc.com/blog/zoom-mkmapview-to-fit-annotations/

(Use it all the time.)

Answer 2

In iOS7 there's a method that does just that. Just call:

[yourMapView showAnnotations:yourAnnotationsArray animated:YES];

Answer 3

Those who do the monotouch c# coding

BasicMapAnnotation is inherit class from MKAnnotation

private void GetRegion(MKMapView mapView)
{
    var userWasVisible = mapView.ShowsUserLocation;
    mapView.ShowsUserLocation = false; // ignoring the blue blip
    // start with the widest possible viewport
    var tl = new CLLocationCoordinate2D(-90, 180); // top left
    var br = new CLLocationCoordinate2D(90, -180); // bottom right
    foreach (var an in mapView.Annotations)
    {
        // narrow the viewport bit-by-bit
        CLLocationCoordinate2D coordinate = ((BasicMapAnnotation) an).Coordinate;
        tl.Longitude = Math.Min(tl.Longitude, coordinate.Longitude);
        tl.Latitude = Math.Max(tl.Latitude, coordinate.Latitude);
        br.Longitude = Math.Max(br.Longitude, coordinate.Longitude);
        br.Latitude = Math.Min(br.Latitude, coordinate.Latitude);
    }
    var center = new CLLocationCoordinate2D
    {
        // divide the range by two to get the center
        Latitude = tl.Latitude - (tl.Latitude - br.Latitude)*0.5,Longitude = tl.Longitude + (br.Longitude - tl.Longitude)*0.5

    };
    var span = new MKCoordinateSpan
    {
        // calculate the span, with 20% margin so pins aren’t on the edge
        LatitudeDelta = Math.Abs(tl.Latitude - br.Latitude)*1.2,LongitudeDelta = Math.Abs(br.Longitude - tl.Longitude)*1.2

    };
    var region = new MKCoordinateRegion {Center = center, Span = span};
    region = mapView.RegionThatFits(region); // adjusts zoom level too
                mapView.SetRegion(region, true); // animated transition
                mapView.ShowsUserLocation =

    userWasVisible;

}

Answer 4

You can use this code to show all annotations

MKMapRect zoomRect = MKMapRectNull;
for (id <MKAnnotation> annotation in mapView.annotations)
{
    MKMapPoint annotationPoint = MKMapPointForCoordinate(annotation.coordinate);
    MKMapRect pointRect = MKMapRectMake(annotationPoint.x, annotationPoint.y, 0.1, 0.1);
    zoomRect = MKMapRectUnion(zoomRect, pointRect);
}
[mapView setVisibleMapRect:zoomRect animated:YES];

if you want to include user location just replace two lines below with the first line of above code

MKMapPoint annotationPoint = MKMapPointForCoordinate(mapView.userLocation.coordinate);
MKMapRect zoomRect = MKMapRectMake(annotationPoint.x, annotationPoint.y, 0.1, 0.1);