Math is sort of hierarchical in that advanced maths depend on earlier math learning. But the overall map is more a huge confused network, with topics splitting and feeding into each other all over the place. I am going to repeat my regular recommendation, if you want to study maths on your own, do some reading about math. My recommendation, as always, is Philip Davis and Reuben Hersh, The Mathematical Experience. It is the broadest discussion of maths that I know of. I haven't seen the new edition which has been enlarged and with exercises for studying, but that is mostly intended (from the reviews) for college students' only exposure to math, and if you intend to continue studying math, I don't really think it is necessary.