iOS Scroll to coordinate and zoom-level


Example

When you show a location to your users, you might want the MKMapView to display a coordinate at a zoom-level instead of setting a region to show. This functionality is not implemented by default, so you need to extend MKMapView with a methods that do the complex calculation from a coordinate and zoom-level to a MKCoordinateRegion.

let MERCATOR_OFFSET = 268435456.0
let MERCATOR_RADIUS = 85445659.44705395
let DEGREES = 180.0

public extension MKMapView {
    
    //MARK: Map Conversion Methods
    
    private func longitudeToPixelSpaceX(longitude:Double)->Double{
        return round(MERCATOR_OFFSET + MERCATOR_RADIUS * longitude * M_PI / DEGREES)
    }
    
    private func latitudeToPixelSpaceY(latitude:Double)->Double{
        return round(MERCATOR_OFFSET - MERCATOR_RADIUS * log((1 + sin(latitude * M_PI / DEGREES)) / (1 - sin(latitude * M_PI / DEGREES))) / 2.0)
    }
    
    private func pixelSpaceXToLongitude(pixelX:Double)->Double{
        return ((round(pixelX) - MERCATOR_OFFSET) / MERCATOR_RADIUS) * DEGREES / M_PI
    }
    
    private func pixelSpaceYToLatitude(pixelY:Double)->Double{
        return (M_PI / 2.0 - 2.0 * atan(exp((round(pixelY) - MERCATOR_OFFSET) / MERCATOR_RADIUS))) * DEGREES / M_PI
    }
    
    private func coordinateSpanWithCenterCoordinate(centerCoordinate:CLLocationCoordinate2D, zoomLevel:Double)->MKCoordinateSpan{
        // convert center coordiate to pixel space
        let centerPixelX = longitudeToPixelSpaceX(longitude: centerCoordinate.longitude)
        let centerPixelY = latitudeToPixelSpaceY(latitude: centerCoordinate.latitude)
        print(centerCoordinate)
        // determine the scale value from the zoom level
        let zoomExponent:Double = 20.0 - zoomLevel
        let zoomScale:Double = pow(2.0, zoomExponent)
        // scale the map’s size in pixel space
        let mapSizeInPixels = self.bounds.size
        let scaledMapWidth = Double(mapSizeInPixels.width) * zoomScale
        let scaledMapHeight = Double(mapSizeInPixels.height) * zoomScale
        // figure out the position of the top-left pixel
        let topLeftPixelX = centerPixelX - (scaledMapWidth / 2.0)
        let topLeftPixelY = centerPixelY - (scaledMapHeight / 2.0)
        // find delta between left and right longitudes
        let minLng = pixelSpaceXToLongitude(pixelX: topLeftPixelX)
        let maxLng = pixelSpaceXToLongitude(pixelX: topLeftPixelX + scaledMapWidth)
        let longitudeDelta = maxLng - minLng
        let minLat = pixelSpaceYToLatitude(pixelY: topLeftPixelY)
        let maxLat = pixelSpaceYToLatitude(pixelY: topLeftPixelY + scaledMapHeight)
        let latitudeDelta = -1.0 * (maxLat - minLat)
        return MKCoordinateSpan(latitudeDelta: latitudeDelta, longitudeDelta: longitudeDelta)
    }
    
    /**
     Sets the center of the `MKMapView` to a `CLLocationCoordinate2D` with a custom zoom-level. There is no nee to set a region manually. :-)
     
     - author: Mylene Bayan (on GitHub)
     */
    public func setCenter(_ coordinate:CLLocationCoordinate2D, zoomLevel:Double, animated:Bool){
        // clamp large numbers to 28
        var zoomLevel = zoomLevel
        zoomLevel = min(zoomLevel, 28)
        // use the zoom level to compute the region
        print(coordinate)
        let span = self.coordinateSpanWithCenterCoordinate(centerCoordinate: coordinate, zoomLevel: zoomLevel)
        let region = MKCoordinateRegionMake(coordinate, span)
        if region.center.longitude == -180.00000000{
            print("Invalid Region")
        }
        else{
            self.setRegion(region, animated: animated)
        }
    }
}

(The original Swift 2 version by Mylene Bayan can be found on GitHub)

After you implemented this extension, you can set the center coordinate as following:

let centerCoordinate = CLLocationCoordinate2DMake(48.136315, 11.5752901) //latitude, longitude
mapView?.setCenter(centerCoordinate, zoomLevel: 15, animated: true)

zoomLevel is a Double value, usually between 0 and 21 (which is a very high zoom-level), but values up to 28 are allowed.