title: offline retina map tiles too big
body: <p>This question has no answer since august.
  I've found no question identical.
  I hope it's clear enough.
  There seems to be few questions on maps but someone must know the answer.</p>
  
  <p>I'm trying to display an offline map using 512x512 tiles. I have the tiles named like 22524@x2.png
  if I use the 256x256 tiles the map displays correctly, but the 512 tiles only show a quarter of each tile. 
  here's my code</p>
  
  <pre><code>//Get the URL template to the map tiles
  let baseURL = NSBundle.mainBundle().bundleURL.absoluteString
  
  //let urlTemplate = baseURL.stringByAppendingString("osmm/{z}/{x}/{y}.png/")
  let urlTemplate = baseURL.stringByAppendingString("two/{z}/{x}/{y}@2x.png/")
  
  print(urlTemplate)
  
  
  let carte_indice = MKTileOverlay(URLTemplate:urlTemplate)
  
  carte_indice.geometryFlipped = false
  
  carte_indice.canReplaceMapContent = true
  
  carte_indice.maximumZ = 18
  carte_indice.minimumZ = 16
  
  
  
  self.mapView.addOverlay(carte_indice)
  </code></pre>
  
  <p>What do I need to add to get the tiles to display correctly? 
  Is a map using 256x256 tiles on a retina screen acceptable  by apple?</p>