Today's xkcd suggests geohashing - using the date and Dow opening to generate a random physical location for a meetup.  It's fun to think about this method being used to coordinate Ephemerisle gatherings.  I can see the method being both better and worse on the ocean because of it's relative homogeneity - every place is like every other place.  So you don't have the failure mode of randomly generating a location that's difficult or impossible to reach, but you don't get