I never learned much about mapping or map projections until university, I still think it's one of the most valuable things I learned there and one of the things I learned actually worth the money.

We had a couple courses on manual mapping, surveying, geography, compass reading triangulation, all that stuff. How to draw a map by hand based on compass and survey data.

By far some of the most awesome stuff i've learned. I agree, more stuff like this should be touched on in high school. Mapping is such a large yet underappreciated part of society.