Controller Mapping for Unusual Systems

How are people mapping systems like Atari 5200, Astrocade, ColecoVision, etc?

I am having a hard time figuring this out.

I don’t personally use any of those cores, but as a basic workflow, I typically check the docs to see what the default mappings are: and then try the default map and only change them if I find a problem with it, as most cores are designed around a “sane” default mapping.