iOS MKMapView zoom to show all markers

Question

I'm working with MKMapView and have plotted several points on the map. I have used the MKCoordinateRegion and MKCoordinateSpan to enable zooming etc around one of the points - but that's not what I want...

I'm trying to use something similar to the Javascript zoom to bounds function. so all my points should be visible to the user. (There will be around 10 points around the UK) I'd like to show them all, or if most of them were in the London area, zoom to there.

Is there a way to work this out programatically?

Answer 1

Sure. You want to find the biggest and smallest latitude and longitude values among your annotations (which you can do by iterating over map.annotations), then set the map to show all of them.

// pad our map by 10% around the farthest annotations
#define MAP_PADDING 1.1

// we'll make sure that our minimum vertical span is about a kilometer
// there are ~111km to a degree of latitude. regionThatFits will take care of
// longitude, which is more complicated, anyway. 
#define MINIMUM_VISIBLE_LATITUDE 0.01

MKCoordinateRegion region;
region.center.latitude = (minLatitude + maxLatitude) / 2;
region.center.longitude = (minLongitude + maxLongitude) / 2;

region.span.latitudeDelta = (maxLatitude - minLatitude) * MAP_PADDING;

region.span.latitudeDelta = (region.span.latitudeDelta < MINIMUM_VISIBLE_LATITUDE)
    ? MINIMUM_VISIBLE_LATITUDE 
    : region.span.latitudeDelta;

region.span.longitudeDelta = (maxLongitude - minLongitude) * MAP_PADDING;

MKCoordinateRegion scaledRegion = [map regionThatFits:region];
[map setRegion:scaledRegion animated:YES];