It appears that no great diagram is solely authored by its creator. Most of those described here were the culmination of centuries of accumulated knowledge. Most arose from collaboration (and oftentimes in competition) with others. Each was a product and a reflection of its unique cultural, historical and political environment. Each represented specific preoccupations, interests, and stake holders.
The great diagrams depicted in the book form the basis for many fields — art, astronomy, cartography, chemistry, mathematics, engineering, history, communications, particle physics, and space travel among others. More often than not, however, their creators — mostly known, but many lost to time — were polymaths who are creating new technologies or breakthroughs by drawing from a potent combination of disciplines. By applying trigonometric methods to the heavens, or by harnessing the movement of the sun and the planets to keep time, they were forging powerful new tools; their diagrams were imbued with synergy.
Christianson offers a definition:
From the latin diagramma (figure) from Greek, a figure worked out b lines, plan, from diagraphein, from graphein to write.
First known use of the word: 1619.
A plan, a sketch, drawing, outline, not necessarily representational, designed to demonstrate or explain something or clarify the relationship existing between the parts of the whole.
In mathematics, a graphic representation of an algebraic or geometric relationship. A chart or graph.
A drawing or plan that outlines and explains the parts, operation, etc. of something: a diagram of an engine.