That's very interesting. I know the editor of Tor books in the UK, who publish China Mieville. I had a moan to him about the state of maps in SF and F novels; particularly those drawn by the author. He said that in many cases (I don't know if Perdido St Station was one of them) the publisher had a professional draw the map in prefrence to the map produced by the author. Once you've finished this one, I'll email it to the editor if you like!

Good luck with the project aero - Cities have so much in them so to do a good one with lots of detail must take ages.