Because you can't add roads, this is something you have to plan for ahead of time.
I'd request either the ability to add roads (I'm sure that might be complicated) or the option to replace the background image with a new one.
Then as the map changes for my games, I can upload new images to update in the background!
That is a very good idea!
Drawing road will be a feature for a more distant future as there are more pressing issues. But replacing the background image should be possible without too much hassle. Will be included in the roadmap for the 0.4 update.
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Oh, and of course I will need post the roadmap first.