A treemap view shows the hierarchical structure of the document as boxes within boxes, taking up the entire window. You can re-structure the hierarchy of the document in a treemap window by dragging the box representing a note (and the boxes it contains) into another box in the window. A treemap view does not show any of the links in the document. A treemap view doesn't differentiate between notes and agents as in outline or map view. Treemap dog-ears do show the ageing colour.
If a box has too many children to display each nested within the containing (parent) box, the parent box's internal layout is 'greeked' out and shown filled with a tint of $Color. Clicking such a greeked box sets focus on the parent note but if you double click, the map navigates 'down' a layer. Use the normal 'up' button to return.
If the map window is dragged larger, some boxes may un-greek themselves. Enlarging the physical window may sometimes be more useful than navigating up/down the hierarchy in a smaller viewing port.
As with other views, the dog-ears yellow over time.