TITLE: Great mathematical figures and/or diagrams?
QUESTION [48 upvotes]: Most math papers have few figures, if any, although sometimes a well-chosen figure can be a tremendous help in understanding mathematical concepts. Does anyone have any examples of notable uses of figures in mathematical writing and/or texts that make great use of figures/diagrams/illustrations?

REPLY [3 votes]: In my opinion, a book that sets a new standard, not only in the quality of the pictures, but in overall design is A singular mathematical promenade by Étienne Ghys. A free PDF of the book is available here:
http://perso.ens-lyon.fr/ghys/promenade/
The pictures are in fact more vivid in the PDF version than on paper.