Cool map Robulous, I'd like to see how this one turns out. The closest thing I've seen to a vertical city is Schley's Diyun or that fantasy tower city that was losely based on Kowloon Walled City a few months back.

I'm with Larb on the absence of a spiralling main "street", but I don't think that it detracts from the map. What does confuse me is the lack of dotted lines showing where the throat and the conduit lead to the magma chamber in the volcano. If your city is built around the crater, there should be something there to indicate it. Otherwise it just looks like a vertical city in an upthrusting finger of rock.

Something else that would be cool is an inset or two of a critical area showing residences, important buildings, etc.

Keep at it, this looks like it is going to be one very cool map.