Filter Catagories question

I'm sure this has come up before, but I searched quite extensively, and could not find anything about it.

My 'simple' question is this: Is there a list of criteria somewhere, regarding exactly what defines the catagory into which a filter will be placed?

I only ask because I have tried 3 times to get a filter into the 'photo' catagory, but all 3 ended up in the 'miscellaneous' catagory.

This also brought up a few other thoughts. For instance: Which catagory is most or least popular? I suspect the 'photo' catagory is probably the most popular, but it certainly wouldn't be the first or last time if I was wrong.

I would think it would be useful to know what defines these catagories somewhat, and not simply for the purpose of putting more filters in the popular catagories, but perhaps the very opposite... putting good filters into the less popular catagories might attract an under-explored user base.

On a final note: knowing which catagories are most or least developed might also help. I'm sure there are some users who would love the challenge of creating excellent filters for the under-developed areas of the library.

Thanks for reading!