Systems

If by 'system' is meant — and this is the minimal sense of the word — a sort of consequence, coherence and insistence — a certain gathering together — there is an injunction to the system that I have never renounced, and never wished to. … 'System ', however, in a philosophical sense that is more rigorous, and perhaps more modern, can also be taken to mean a totalization in the configuration, a continuity of all statements, a form of coherence (not coherence itself), involving syllogicity of logic, a certain syn which is no longer simply that of gathering in general, but rather of the assemblage of ontological propositions.

— Derrida and Ferraris, I Have a Taste for the 

Secret, (Polity Press, 2001), p. 3

Diagrammatic thinking, at least as I envision it, is also an effort to get away from the "system" as an axiomatic, analytically formal, would-be universal "totalization" and to see it as a particular collection of indices and relationships abstracted from experience on the one side and limited in its applications to that kind of experience on the other.

And, such "systems" occur on much simpler levels still. Andrew Whiten's "intervening variable":

Andrew Whiten, "Triangulation, Intervening Variables, and Experience
Projection," Behavioral and Brain Sciences 21 (1) (1998):133

performs the same mediating function in what he calls the "triangulation" of patterns on the one side with consequences on the other.  It really doesn't matter exactly what the intervening variable is — whether it's a word, an image, or a layer of neurons.  What matters is that it's operating diagrammatically with "a sort of consequence, coherence and insistence — a certain gathering together."

Maps, Cameras, and Ideology

Maps as diagrams are judged by how well they function, but that functionality, however it's defined, is guaranteed by the precision and accuracy that goes into the map's making.  A large part of why Captain James Cook rise from below decks to command of three exploratory expeditions to the South Pacific was his mapmaking abilities, and the maps he made were so precise and accurate, I've heard, that they were still being used in some places at the start of WW II.  This emphasis on the accuracy and precision is generally associated with scientific maps.

But there are also persuasive maps.  And with these the accuracy and precision, that is, how much of it is really needed, is measured by the function of the map. Like Marx's metaphor of the camera obscura:

If in all ideology men and their circumstances appear upside own as in a camera obscura, this phenomenon arises just as much for their historical life-process as the inversion of objects on the retina does from their physical life-process. — Karl Marx, The German Ideology, 1844, p.47

the process inverts things.  Instead of the accuracy and precision of the map being the basis for it's functionality, its functionality is the basis for how much accuracy and precision there needs to be.  With science and ideology, or to put it more generally, the inversion is from truth being the basis for acceptance to acceptance being the basis for truth.

And, the camera metaphor also holds up when we consider accuracy and precision in relation to functionless maps hanging on a wall or illustrating a book.  Perhaps the exactness has an aesthetic quality to it, but like the digital accuracy of the universe of photographs now being stored online, it has been rendered inane.

Image or Diagram

The Mercator map developed in 1569 was well-suited for seafaring.  A course plotted anywhere on the map matches up with the bearing the ship needs to take in getting from one place to another.  To be truly useful the Mercator map needed to be supplemented by a marine chronometer and a knowledge of the magnetic versus geographical poles, but as a diagram the consequences drawn from its applications were verified and refined by countless navigators.  However, as a result of its success, the Mercator projection of the world came to represent the world for virtually everyone.  The diagram used by sailors became the image in books and classrooms everywhere.

The basis for accepting or rejecting an image is the connection between it and the object it represents.  The map, as an image, should be a precise and accurate representation of that object.  It can be criticized for distorting what it represents, as the Mercator map has been for distorting distances and sizes.  It can be admonished for embellishing or channelling what it represents with subliminal messages regarding other things.  It can be argued that the connection between a map and its object should be more inclusive and exact like a camera or more exclusive and ambiguous like art.  The map as a diagram is also based on an analogy to the object it represents, and that analogy can also be critically assessed; but it, and its analogy, are accepted or rejected on the basis of their functionality.  Diagrams, unlike images, answer to what can be done with them, to how well they work in subsequent applications of it, not to their derivation from, or representation of, the object.