Hypothetigraphy

Many theories of diagrams are limited in scope to just one or two manifestations of abstract drawings. Diagrammatic representation of numerical data has been well studied since Edward Tufte's Visual Display of Quantitative Information, but stemmatic drawings like the Great Stemma are rarely well explained. I have been impressed at the theoretical work of Manfredo Massironi (1937-) of the University of Verona in Italy. Massironi has devised a concept he calls hypothetigraphy to describe drawings that present hypothetical, invisible, abstract ideas. It is presented in his 2002 book, The psychology of graphic images: seeing, drawing, communicating (Link: Google Books). (The English translation from the Italian is not perfect, and sometimes makes no sense: the term itself is sometimes spelled "hypothesigraphy" in the text, varying in orthography from one line to the next (e.g. p. 164), but "hypothetigraphy" is the form used in the headings and index.)

He says he departs from the idea that "illustrating is a way of emphasizing, by visual means, those contents that cannot be effectively conveyed by verbal expression." He proposes that hypothetigraphy has two roles: (a) a connective function (connecting into a unitary pattern a body of knowledge [which is] fragmented and apparently not well organized) and (b) a reconstructive function (reconstructing the various phases of a process for purposes of illustration and interpretation, starting from observable results).

According to my definition, hypothetigraphy defines a rather homogenenous class of drawings, which I call hypothetigraphs ....
The first feature, and one that is most easily noted, is the use of simple geometric figures.... The "true" objects and their appearance are not important in this endeavor, for the phenomena under consideration have to do with relationships and with dynamic interactions between elements.... The shape of elements per se is usually an irrelevant piece of information, which is best left out or represented simply by the most abstract of shapes, the circle.
A second and most immediately noticeable feature of hypothetigraphs is the addition of brief written text to the picture.... The inclusion of written text is always necessary in hypothetigraphy which would otherwise lose its communicative function... Verbal and visual information are inextricably and necessarily connected.
Another distinguishing feature of hypothetigraphy is the the almost exclusive use of precise marks, drawn using the ruler ... Precise, clear lines contribute in conveying the impression that the depicted forms are mental constructs, not representations of natural objects.
Typical of hypothetigraphy is ... the use of object lines ... Object lines are not used to mimic some aspect of reality but to illustrate relationships, correspondences or connections.... Relationships and connections and trajectories ... lend themselves naturally to an interpretation in terms of threads, ropes and connecting cables.
A fifth feature of hypothetigraphy is the number of represented dimensions, which tends to be as small as possible within the constraints of the logic of the representation.
Finally, hypothetigraphy tends to place the viewpoint frontally relative to the picture plane, an tends to present figures without a background.... The second of these ... contributes to focus the attention of the viewer, avoiding unwanted contextual effects.

This is all very useful. The six "features" listed above are all applicable to the Great Stemma:

1. Its graphic elements are circles of various sizes. They do not represent heads or anything else physical but are entirely abstract, representing generations and dynasties.
2. Text within the roundels, along the connecting lines and in the final Sicut Lucas evangelista section, is there to expand the effect of the drawn figures.
3. Its lines are generally straight, except for the final meeting of the two fila, and the whole structure is drawn with a certain sterility to emphasize its abstract meaning.
4. The connecting lines represent succession, and ramifications where necessary.
5. The drawing is strictly two dimensional
6. It has no background colour or images. My attachment of a yellow timeline band to the reconstruction is in fact out of harmony with the austerity of the original.

Massironi makes no mention of the Great Stemma. In fact he does not mention any stemmatic drawings at all. But his observations are so acute that they apply to the stemma without any modification being required of them.