I'll fix the desert zone issue, as for opacity the islands should be layered on-top of the biome layer, unless you mean the zone highlighting.
The biomes as-is are not final as I try to figure out a better solution.
Layer Control, this control allows for changing which layers are shown on the map.
Zoom, this control allows you to zoom the map in or out.
Right clicking the map will show the in-game GPS coordinates rounded to two digits.
This has been added.