This will take some thought and may possibly be another 2 monther.

The participants each start a map and work on it for a given period. Then, what they have started is passed on to another participant either on a partner basis or on a rotational basis. I like the partner basis where two people swap maps (so long as there's an even number) but nobody knows who their partner is until the end of the first phase. The other option is to pass your map to the person sat at the left, so to speak. i.e. you have 7 people in the challenge. Number 1 passes to number 2, who passes their to number 3, etc. until number 7 passes to number 1.

I don't know how the compass would be awarded - that's a headache for the CLs to work out