okay so here's a weird question. scott mccloud's "big triangle"— https://wordsonplay.com/2009/10/the-big-triangle/ is there a general term for this kind of thing? a space with extremes where items in the space are annotated with illustrations/representations whose position in the space corresponds to the extent to which the properties at the extremes describe them?
e.g., eadweard muybridge photo illustrations (if you unwrapped them into a single line) http://www.eadweardmuybridge.co.uk/ would be a one-dimensional example of this (where the dimension represents time); t-sne visualizations would be another example (where the dimensions don't have a set meaning) https://lvdmaaten.github.io/tsne/ maybe even the periodic table of elements would qualify https://en.wikipedia.org/wiki/Periodic_table (though in that case the "representations" are just the names of the elements)
the new york magazine approval matrix is another example http://nymag.com/arts/all/approvalmatrix/approval-matrix-2017-03-20/
and the covers of animorphs books https://duckduckgo.com/?q=animorphs&t=ffab&iax=images&ia=images
related, it looks like the only critical writing on animorphs comes in the form of pay-to-download "homework help" book reports http://www.bookrags.com/studyguide-animorphs-4/style.html#gsc.tab=0
oh okay this is this is helpful (on the topic of visualization, not on the topic of critical writing on animorphs) still not exactly what I'm looking for though, oh well https://onlinelibrary.wiley.com/doi/abs/10.1002/jhbs.20078
@ansate ha, nice! actually what I'm looking for is the earliest known example of an illustration showing intermediate stages of transformation from one thing to another (when that transformation *isn't* time based, a la https://en.wikipedia.org/wiki/March_of_Progress) so really only the *covers* of animorphs are of particular interest at this point
Mark Twain's 19th-century animorphs https://en.wikipedia.org/wiki/March_of_Progress#/media/File:Connecticut_yankee_evolution.jpg