[this is the third segment of a post started here (part 1), and continued here (part 2)]
Mind maps were the most popular type of diagram. By the time universities emerged towards the end of the 12th century, diagrams had become the main tool for organising information and knowledge. A way to understand the human soul (anima) was through complex diagrams linking Aristotelian theory with modern (i.e. medieval) ideas.
A complex zoomorphic diagram connecting elements of ethics, kinship, law and theology, Cotton Roll XIV 12, membrane 37.
Diagrams offered an overview of various fields of knowledge, like language, rhetoric, logic, maths, astronomy or music. They fostered abstraction and the view from above, which accustoms the human mind to look at things lying beyond the field of vision.
The development of cartography tracks the evolution of diagrams closely. Admittedly, maps already existed in the ancient world, but the science of mapmaking emerged in the medieval period. Maps are views from above, using an abstract representation to model a field lying beyond the field of vision. While a diagram of the universe, like in Harley MS 647 (see image above), projects a theoretical model independent of empirical observation (notwithstanding occasional medieval stargazing), a nautical map is an abstraction derived from experience.