Swift - Scale up low resolution map tiles to show on retina screens

gistfile1.swift

// Somewhere in ViewController:

	func changeMapOverlay() {
		
		mapOverlay = MyTileOverlay( URLTemplate: "http://tile.openstreetmap.org/{z}/{x}/{y}.png" )
		mapOverlay!.canReplaceMapContent = true
		mapOverlay!.tileSize = CGSize( width: 512, height: 512 )
		
		self.mapView.addOverlay( self.mapOverlay, level: .AboveLabels )
		
	}


class MyTileOverlay: MKTileOverlay {
	
	override func loadTileAtPath(path: MKTileOverlayPath, result: ((NSData!, NSError!) -> Void)!) {
		
		super.loadTileAtPath( path ) { ( data, error ) in
			
			let tileImage = UIImage( data: data )
			let scale: CGFloat = 1.0
			let sizeChange = CGSize( width: 512, height: 512 )
			
			UIGraphicsBeginImageContextWithOptions( sizeChange, false, scale )
			tileImage!.drawInRect( CGRect(origin: CGPointZero, size: sizeChange) )
			
			let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
			
			result( UIImagePNGRepresentation( scaledImage ), error )
			
		}
		
	}
	
}