A couple things I have been thinking about recently, which come together in this: even dreams typically have a location, but it is a unique quality of dreams, at least the ones I have been having lately, to feature a location in isolation, that is separated from character or context; and: in matters of taxonomy, more than three levels is seldom viable in practical terms, but two is seldom sufficient.
In the work I am currently involved in developing a financial application, I see a three-level vocabulary emerging which I have witnessed in other domains, typified as category, type and subtype.
If I was attempting to describe an ontology of dreams, therefore, I imagine I would use a category of "location", a type of location name or "realm", and a subtype describing each specific "locale" within the realm. So, for instance:
What I would like to do is build an API, attached to a cloud storage, to allow people to describe their own dream landscapes in these terms. More on this as it develops. Please comment as you see fit.