This video makes a good stab at mapping out the entire subject. Something like this would be a useful addition to all maths courses.
I’d really like to understand WHY we have selected some bits for inclusion in public exam curricula and left other bits out. My suspicion is that it’s based on the preferences of various senior academics. As usual, these political types don’t care much about whether this material will actually help young people -either in daily life or in higher study.
This contributes to the feeling that studying maths is about gathering a basketful of disconnected tools. It should be more integrated -and having in mind the big picture would greatly help.