Zoom into and center the MKAnnotations on an MKMapView with one line. With our without animation.

MKMapViewExtensions.swift

/**
    MKMapViewExtensions.swift
    
    Zoom into and center the MKAnnotations on an MKMapView with one line. With our without animation.
    
    <https://gist.github.com/tannernelson/45741c070508f081657a>
*/

import MapKit

extension MKMapView {

    func zoomToAnnotations(animated: Bool) {
        var zoomRect = MKMapRectNull
        for annotation in self.annotations {
            if let annotation = annotation as? MKAnnotation {
                let annotationPoint = MKMapPointForCoordinate(annotation.coordinate)
                let pointRect = MKMapRectMake(annotationPoint.x, annotationPoint.y, 0.1, 0.1)
                if MKMapRectIsNull(zoomRect) {
                    zoomRect = pointRect
                } else {
                    zoomRect = MKMapRectUnion(zoomRect, pointRect)
                }
            }
        }
        
        let padding = 0.1
        
        let addHeight = zoomRect.size.height * (1 + padding)
        let addWidth = zoomRect.size.width * (1 + padding)
        
        zoomRect.size.height += addHeight
        zoomRect.size.width += addWidth
        
        zoomRect.origin.x -= addWidth / 2
        zoomRect.origin.y -= addHeight / 2
        
        self.setVisibleMapRect(zoomRect, animated: animated)
    }

}