It seems to be a bit of a kludge.
Firstly, you replace the map with an overlay of your own...
self.mapView.insertOverlay(underlay, at: 0, level: MKOverlayLevel.aboveLabels)
This can be anything. If you want to use Google Maps, or Open Street Map, you can, like this:
let url = "http://mt0.google.com/vt/x={x}&y={y}&z={z}"
//let url = "http://c.tile.openstreetmap.org/{z}/{x}/{y}.png"
let underlay = MKTileOverlay(urlTemplate: url)
underlay.canReplaceMapContent = true
alternatively, if you just want blank, give it a default layer:
let underlay = MKTileOverlay()
underlay.canReplaceMapContent = true
The parameter level:
allows you to specify whether your background obscures just their background map, or the background & roads or the background & labels, but NOT above everything. The documentation says:
MKOverlayLevel.aboveLabels
case aboveLabels = 1
Place the overlay above map labels, shields, or point-of-interest
icons but below annotations and 3D projections of buildings.
I can't get that to work for the default MKTileOverlay()
- it seems to do the same as the alternative .aboveRoads
- i.e. it hides all of the map including roads, but not labels. When you specify one of the external overlays (e.g. google) - they DO replace the labels. Probably a bug, so the final step, to completely obliterate the labels is
self.mapView.mapType = .satellite
This removes the labels, and your overlay is hiding the satellite map. Not neat, but not difficult, either.