Positioning MKMapView to show multiple annotations at once

Question

I've got several annotations I want to add to my MKMapView (it could 0-n items, where n is generally around 5). I can add the annotations fine, but I want to resize the map to fit all annotations onscreen at once, and I'm not sure how to do this.

I've been looking at -regionThatFits: but I'm not quite sure what to do with it. I'll post some code to show what I've got so far. I think this should be a generally straightforward task but I'm feeling a bit overwhelmed with MapKit so far.

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation{

location = newLocation.coordinate;
//One location is obtained.. just zoom to that location

MKCoordinateRegion region;
region.center = location;

//Set Zoom level using Span
MKCoordinateSpan span;
span.latitudeDelta = 0.015;
span.longitudeDelta = 0.015;
region.span = span;
// Set the region here... but I want this to be a dynamic size
// Obviously this should be set after I've added my annotations
[mapView setRegion:region animated:YES];

// Test data, using these as annotations for now
NSArray *arr = [NSArray arrayWithObjects:@"one", @"two", @"three", @"four", nil];
float ex = 0.01;
for (NSString *s in arr) {
    JBAnnotation *placemark = [[JBAnnotation alloc] initWithLat:(location.latitude + ex) lon:location.longitude];
 [mapView addAnnotation:placemark];
 ex = ex + 0.005;
}
    // What do I do here?
    [mapView setRegion:[mapView regionThatFits:region] animated:YES];
}

Notice, this all happens as I receive a location update... I don't know if that's an appropriate place to do this. If not, where would be a better place? -viewDidLoad?

Thanks in advance.

Answer 1

One possible solution might be measuring the distance between the current location and all the annotations and using the MKCoordinateRegionMakeWithDistance method to make a region that has a slightly greater distance than the furthest annotation.

This would of course get slower the more annotations you added though.

Answer 2

I have done something similiar to this to zoom out (or in) to an area that included a point annotation and the current location. You could expand this by looping through your annotations.

The basic steps are:

• Calculate the min lat/long
  
• Calculate the max lat/long
  
• Create CLLocation objects for these two points
  
• Calculate distance between points
  
• Create region using center point between points and distance converted to degrees
  
• Pass region into MapView to adjust
  
• Use adjusted region to set MapView region
  

    -(IBAction)zoomOut:(id)sender {

        CLLocationCoordinate2D southWest = _newLocation.coordinate;
        CLLocationCoordinate2D northEast = southWest;

        southWest.latitude = MIN(southWest.latitude, _annotation.coordinate.latitude);
        southWest.longitude = MIN(southWest.longitude, _annotation.coordinate.longitude);

        northEast.latitude = MAX(northEast.latitude, _annotation.coordinate.latitude);
        northEast.longitude = MAX(northEast.longitude, _annotation.coordinate.longitude);

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

        // This is a diag distance (if you wanted tighter you could do NE-NW or NE-SE)
        CLLocationDistance meters = [locSouthWest getDistanceFrom: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 = 0.0;

        _savedRegion = [_mapView regionThatFits:region];
        [_mapView setRegion:_savedRegion animated:YES];

        [locSouthWest release];
        [locNorthEast release];
    }

Answer 3

Take a look at http://codisllc.com/blog/zoom-mkmapview-to-fit-annotations/

I couldn't get the code above to work correctly, but this does. Enjoy!

Answer 4

Hello jbrennan

Having same issue.. I want to display / resize the map to fit all annotations at once in the MapView Screen. Could you please post the example of code which does this? or PLEASE send by email [email protected]