Currently it's a bit unintuitive how to render other dimensions.

I have a world, that only contains a Nether map. This is not picked up. Instead what I have to do is copy the level.dat into the DIM-1 folder, and point BlueMap towards that.

Ah yes, i missed that probably because i only tested other dimensions with sponge and sponge organizes its dimensions as individual worlds (i think?)

@Katrix
So with ee38432 it will now search in the parent folder for the level.dat if it doesn't find one in the world folder, so you don't have to copy that.
You will still need to configure the world/DIM-1 folder.
I think that is a cleaner and more flexible solution than making a "dimension" configuration or something.
What do you think? Is it easy enough that way?

Yeah, seems like a good solution, so closing this issue.