Let's say you're trying to solve a real life problem, but you don't know what kind of maths would be helpful, how do you find the maths concepts involved?
A trivial example: you want to know the slope of a hill you're climbing, but you've never heard of trigonometry. Is there a maths encyclopedia you can look up something like "how to find how steep something is"?
That's a simple example, but imagine it's something more complicated. You know what the problem is, but not what maths is involved, where would you search for this? Maths articles? Research databases? Do you have to call up a mathematician?
I feel like maths is this giant forest and you need like 3 specific trees for your particular problem but good luck figuring out where they are without spending 30 years studying the entire forest first.

Maybe what I'm really asking is where do researchers look? What databases do they search? Are there books not on specific topics but like, a map of maths as a whole?