Hiding the map icon viewport in containers & agents
One last trick, not really related to the above but useful for tidying up a map. In the outline, notice note 'nn' is a container but in the map, its icon (bottom left) has no viewport. How's that done? It is actually quite simple. We set $TitleHeight = $Height, effectively hiding the viewport. $TitleHeight controls the vertical depth of the icon caption area. Notice that the bottom corners of the 'nn' icon are still rounded so the sharp-eyed should still be able to spot the container-masquerading-as-note on their map. If you lose track of 'hidden' containers, just open the map as an outline and look for any item with a disclosure ('flippy') triangle to the left of the note name.
Fine, but now we have hidden the viewport in 'nn' we cannot drill down as we cannot double-click the viewport area. Another little trick: select 'nn' and then use shortcut [Cmd]+[Opt]+[down-arrow]. Boom! The 'nn' container opens and we see the 'oo' icon. Go back up a level and 'nn' is unchanged and still hiding its content.
The agent 'ag' illustrates the same viewport hiding trick as shown with note container 'nn'. Notice how the agent retains the rounded corners at the top of its icon (for a container the rounded corners are at the bottom of the icon). I also found with the agent that if we set $TitleHeight = $Height, then the (display) name is written a bit too close to the top margin of the icon. Happily, if instead we set $TitleHeight = $Height - 0.1, it looks fine. As that also looks good with containers, using the latter expression is a better one-size-fits-all code for viewport 'hiding'. Note that as borders are drawn inside the width/height of the icon, if you set big borders you may need to reset the $TitleHeight—at least for agents.