I found a few people asking this question and getting answers about what tags are intended for that didn't really prove helpful, so I apologize for asking again if there is a good answer somewhere.
I've been running a large wp site for a year and have accumulated about 1000 different tags. The posts are about art exhibitions, and I've tagged them with the city, country and gallery where the show was held, as well as the names of any artists or curators involved. This is already somewhat helpful, because if you're looking for more exhibitions in a certain city or by a certain artist, it's easy to get all of them in one place. But I'd like to allow users to browse a list of all of the cities, artists and so on as a way of more easily accessing the archive. I already have all of this information in tags, what I need to do is be able to group tags into tag-categories, or put another way to develop a hierarchy, where the tag "city" is higher than the tag "Antwerp".
What's my best bet?
Thanks very much for your help.