http://math.ucr.edu/home/baez/books.html http://math.ucr.edu/home/baez/books.html There are others, but this one explicitly says "Math is a much more diverse

http://math.ucr.edu/home/baez/books.html http://math.ucr.edu/home/baez/books.html There are others, but this one explicitly says "Math is a much more diverse subject than physics, in a way: there are lots of branches you can learn without needing to know other branches first... though you only deeply understand a subject after you see how it relates to all the others!"