The ability to see and change existing categories via Community edit has recently been removed by Google. David Rodecker of RelevantAds pointed out this subtle but interesting change in the Google Maps Community Edit feature that was introduced in March of 2008.
A community editor can still add a category but the ability to know how the business was (sometimes erroneously) categorized and to affect that is now gone. This change apparently occurred last week and was first noticed by LocalSplash.
It is interesting to speculate why Google removed this feature of community editing. David Rodecker and LocalSplash both noted that it allowed them to decide which categories were the most appropriate for their clients. One presumes that the either the information that Google was receiving via the feature was for the most part useless or more likely being used to disadvantage competitors. It did provide default categorization information on unclaimed businesses and was the only communication vehicle to alert Google of obviously miscategorized businesses.
I am not sure that having the ability to edit the category information is useful but knowing the category information of claimed and unclaimed businesses would provide a transparency that would be welcomed.Google Maps limits view of Categories via Community Edits by Mike Blumenthal