Function mappable 

pub fn mappable(view: &View, root: NodeId, area: Area) -> bool

Whether there is a map of root in area at all.

plan’s first question, split out because it is also the one the pane asks on every frame: a directory the deleter has emptied has no map, and taking a picture down is not a redraw to be held back until the view settles. Stated once rather than in the two places that ask it, so they cannot come to disagree about what an empty map is — and it costs nothing to ask, being a rolled-up count already on the node.