Great info and a guest post by Dan Austin over at Mike's this week.

Guest Post: Dan Austin on Google Mapmaker Categories

Categories have been a mess in Google Map Maker for years, as well...

Anyway, mappers have been requesting that Google re-organize the categories into a better system, clean up the categories, add more categories, restore missing categories, correct buggy categories, and create a category hierarchy…

This is complicated by the fact that Local has its own set of categories, some of which are ‘invisible’ in GMM and vice versa, and some of which can only be edited in one interface or the other. Local adds its own categories automatically, for example, turning Park into Park, Parks.
If you have any questions about the above, I'm sure one of our Power Mappers Gregg or Andrew will be by to answer them.