Categories have been a mess in Google Map Maker for years, as well. GMM Issue Tracker allows you to add categories for potential inclusion into GMM (which hopefully bleeds over into Local): http://goo.gl/OT3VO and star for the ones you like the most. Unfortunately, GMM, like so many other ‘community’ initiatives they’ve sponsored, largely ignores the input of mappers in favor of big bug fixes, UI upgrades, pet projects, and of course, figuring out ways to lessen the people part of the GMM community, whether it’s through limiting communication with mappers (that seems to be a big initiative, right now, especially in the forums and on individual edits) or increasing the bots ability to manage the system independently. AKA havoc!
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, which you can see reflected in this forum post: http://goo.gl/GddFb; this spreadsheet: http://goo.gl/M4XMX by a power mapper (not Google); and this Facebook discussion: https://www.facebook.com/groups/mapmaker/ which Rich Hintz manages, and who discusses GMM category problems a lot.
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. There’s a longstanding bug or ‘feature’ that appends gcid:[name of category] to categories that you add through Report a problem, which don’t appear that way in Maps, but are visible as such in MM. I assume that this is because the Maps categories, even the ones you select from the dropdown, are not recognized as such standard categories in MM, so it appends gcid: to indicate it’s a custom category. As happens all too frequently, the POIs in one database can become out of sync with another, resulting in islands of categories, and trying to get them to sync can be a real chore.
There has been an effort toward changing the UI for Maps community edits to be more like GMM, but it will also end up orphaning categories that are only visible in the current UI scheme for community edits, making them inaccessible to everyone but Support.
Additionally, GMM has a Primary category, and Local doesn’t (just like GMM has a field for suites, and Maps basically doesn’t), so arranging the categories can be a delicate affair, especially if you want one of two categories visible on the Local page. (Good luck with that, as whatever you change in GMM appears first).
Last, some categories are locked in GMM and Maps (like Locksmith and Military Area), locking the entire POI from any kind of editing on any interface except for the Dashboard. So basically, you have to use Report this in GMM and try to explain what you’re trying to do in order to ‘fix the categories’, or Other in Maps Report a problem. Sometimes this works, sometimes this doesn’t.
So, usually what I do is go through and try to rationalize the categories myself. If it’s claimed (and this is not always clear from GMM, since there’s no indicator that a page is claimed), I try to mess with the categories as little as possible unless there’s category spam, in which case, I’ll delete and/or replace with more appropriate categories, including custom categories. I try to use standard categories whenever possible, set a primary category that explains what the business primarily is, and then build out custom categories that exceed the five category limit if the listing mandates it. Since all those categories are searchable in Maps, even if they’re not visible, it can enhance a business listing’s ability to turn up. And even when I make all these changes, business owners of claimed listings may not approve of the changes, so that can end up screwing up the categories even more as the changes may not sync back to GMM.
Between the bots adding junk categories (that has been a big problem with hotels in Vegas, as bots aggregate tons of bad categories from unrelated features to the larger hotel POIs, resulting in a big mess of categories), clueless business owners listing product types rather than what they do (i.e. Swatch instead of Watch Store), and Google’s inability to rationalize categories and harmonize all the different databases with different category types, you have a lot of problems.