Hello Rich,
This scheme is for Mappers that want to organize a MapUp in their own town in future. The scheme does'nt need a critical mass of mappers, but the organizer need to find a critical mass of mappers if they organize a MapUp.
Schemer is great if you don't have time now to do a MapUp, but want a reminder someday when you feel bored.
You can add the scheme to your schemer profile by yourself by clicking 'I want to do it' button.
Did not know about the Facebook group, thanks! I've joined it.