Mapping collections to specific JSON files?

[chesterblack]

In the docs it mentions best practices are to map one collection per file (https://docs.gitfig.com/design-sync/file-mappings#one-file-per-collection) but I'm not sure how to do that? The mapping seems to just put everything in whatever file I assign to Variables, or it creates a new file at the root of the repo if I don't map anything.