Does anybody have any idea or literature on sensible ways to visualize a taxonomy that’s not strictly hierarchical? Preferably something simpler to understand than a directed graph. When I Google it all I see is “research” on creating a taxonomy of visualizations, because that’s apparently a difficult and urgent problem. I expect the taxonomies to have dozens to hundreds of elements, and they should be editable by end-users on a web-page.
A very common trick (common enough for people doing it not to be aware that it is what they are doing) is to take a maximal subtree, draw that as a tree, declare the rest of the links ‘crosslinks’ and draw them differently, roughly perpendicular to the tree, and in a different colour. If you have only a small percentage of crosslinks this can work well enough. Of course the details of how to draw the crosslinks are hairy.