Aggregate clustered campsites

[quincylvania]

Often many campsites are mapped, and you can see them all when zoomed in:

But when zoomed out, only one is displayed, and you wouldn't know there are others:

We should somehow display when campsites are clustered like this to indicate that people should zoom in to see more. Maybe a little numeral atop the icon? Bonus points for combing the ref labels, like using a label "10–12" when sites, 10, 11, and 12 are aggregated.

There are plenty more cases where icons intersect and we may want to indicate that, but this is a good case to start with.