adaptive level of detail

[ghost]

Based on the amount of geometry from queries of the current viewbox, adaptively determine how much detail to show with an override slider for more or less.

A good test case for this feature is to navigate to somewhere in rural Alaska at a fairly zoomed-out view. In google maps, these areas might have some local roads but you only see them when fairly zoomed in because they are not paved, but they are the only roads around. You should be able to get an overview of where the roads can take you without being so zoomed in.

Perhaps scale of the feature should be another heuristic for whether to show a given feature or not while zoomed out.