well I think there's a natural hierarchy that emerges from the examples given in the periodic table link. Spatial: line graphs, scatterplots, and even barplots

well I think there's a natural hierarchy that emerges from the examples given in the periodic table link. Spatial: line graphs, scatterplots, and even barplots and pie charts(1-dimensional space). Id throw spectogram and anything with time in there as well. Geographic: maps (this could be a subset of spatial) Graphical: graphs, mind-maps, flow charts, all the other graphs-like charts from the examples Visual Metaphors: those weird examples of they give of steps and a bridge, a slide, etc Those 4 categories alone capture all the examples from the webpage, and there are plenty of subcategories within them. So to me a hierarchy / tree seems like a good choice, which is essentially a directed graph (like you suggested)