So I've just thought of something where a whole load of prompts can be entered onto https://wheelofnames.com/ Then the challenge referee spins the wheel for each entrant and assigns the prompt it stops on. The wheel spin thing can even be live streamed in the Discord server just for fun.

Prompts could be things like:
City state
Archipelago
Continent
Ocean
Medieval burgh

I'm sure others can contribute more prompt ideas

Then everyone goes off with their prompt and maps what they feel best represents it.