You can configure an OpenStreetMap tile server, e.g.:
Name=Smoothness,
URL=https://tile.bbbike.org/osm/bbbike-smoothness/${z}/${x}/${y}.png
or
URL=https://{switch:a,b,c}.tile.bbbike.org/osm/bbbike-smoothness/${z}/${x}/${y}.png
or cut & paste image
URL=https://tile.bbbike.org/osm/bbbike-smoothness/15/17602/10746.png
If isBaseLayer is set to "no", the map will be used as on overlay map.
You can configure the order of maps:
The Map Compare admin console is for experts only. Use it on your on own risk!!!
All values will be stored in a persistent cookie. If you delete all your cookies in the browser, all
your Map Compare preferences will be lost.
For more information about tile servers, please read
https://wiki.openstreetmap.org/wiki/Tiles