CF my longer post. Basically in the USA at least (EU has "database directive") the situation is that "facts" aren't themselves copyrightable but the intuitions / guidelines non-experts (like me) have to go from are very much pre-internet and pre-computers.

In the map case: if I make a map of the coast of Florida by:

- looking at maps A, B, and C

- drawing my own map based on what I learned

...then the publishers of A (B or C) can't come sue me for violating their copyright over the shape of the coast of Florida; they have copyright over their specific depiction of that shape but not the shape itself.

Once you move into all-digital datasets a lot of the grounding assumptions are no longer there (perfect reproduction is easy; the data is more abstract and may only really be representable in one way).