Each of the six books that make up Designa is written by a different author on a specific subject. Since they were originally published separately, there is a little overlap from book to book, but not much.
Book 1 is Celtic Design. It offers numerous examples of the iconic winding knots most identified with Irish rock art and illuminated manuscripts. Explanations of how such designs were/are created are clear and practical.
Book 2, Islamic Design, delves into the geometry of the abstract tiling patterns that adorns medieval mosques and the winding patterns of illuminated copies of the Koran from the same era.
Book 3 discusses different kinds of Curves in art and architecture from wrought iron to paisley patterns.
Book 4, Perspective, veers into more cerebral territory, dealing with three-dimensional illusions in two-dimensional media as well as naturally occurring illusions like mirages and rainbows.
Book 5 explores the concept of Symmetry in every possible way. Different kinds or visual symmetry and more abstract notions of mathematical symmetry are given equal time.
Finally, Book 6 explains the pervasive Golden Section. expressed by the Greek letter "Phi", this same proportion appears over and over in botany, anatomy, painting, and even music. Numerous examples are given on all topics.
The only problem I had with Designia is that it's not quite long enough for full and clear explanations on every point. I think the authors presupposed a certain level of mathematical and/or drafting skill that I personally lack, so I was unable to follow some of the more complicated ideas. Nevertheless, I wish this book's mixture of practicality and abstract musing (or something like it) had been incorporated into the way I was taught math back in high school. I might have appreciated more of it.