There are many node overlapping in the screenshot below which shouldn't happen. The layout algorithm should have taken care of this. It is not clear if it is that 1) the layout is not recalculated, or 2) the layout algorithm doesn't deal with such overlapping.
The decision is to use the d3 tree layout only for debugging purpose before a proper layout is implemented (see #138), so this will be no investigated further.
https://github.com/Vis4Sense/HistoryMap/blob/mv3/src/historymap/hmTreeView.js, which is from https://observablehq.com/@d3/tree/
There are many node overlapping in the screenshot below which shouldn't happen. The layout algorithm should have taken care of this. It is not clear if it is that 1) the layout is not recalculated, or 2) the layout algorithm doesn't deal with such overlapping.