MKMapView extension to center map to coordinates with defined zoom level using Swift language (version 3). Also includes a method to return the current zoom level of a MKMapView object.

MKMapViewExtension.swift

//
//  MKMapViewExtension.swift
//  AutocompleteTextfieldSwift
//
//  Created by Mylene Bayan on 2/22/15.
//  Copyright (c) 2015 MaiLin. All rights reserved.
//

import Foundation
import MapKit


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

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)
        
        // 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)
    }
    
    func setCenterCoordinate(centerCoordinate: CLLocationCoordinate2D, zoomLevel: Double, animated: Bool)
    {
        // clamp large numbers to 28
        let zoomLevel = min(zoomLevel, 28)
        
        // use the zoom level to compute the region
        let span = self.coordinateSpanWithCenterCoordinate(centerCoordinate: centerCoordinate, zoomLevel: zoomLevel)
        let region = MKCoordinateRegionMake(centerCoordinate, span)
        if region.center.longitude == -180.00000000 {
            print("Invalid Region")
        } else {
            self.setRegion(region, animated: animated)
        }
    }
    
    func zoomLevel() -> Int
    {
        return 21 - Int(round(log2(Double(self.region.span.longitudeDelta * MERCATOR_RADIUS * M_PI) / Double(180.0 * self.bounds.size.width))));
    }
}