It's a bit of the public transport system in Hong Kong. My parents were over there at around this time last year and bought back a few bits and pieces. In this case, I mainly used it for the visual style - the chained snake of the lines worked well with the composition of the area that I wanted to cover, and the colours complimented the piece by balancing the fine blue matrix of the envelope inside on the top right corner.
I've always had a thing about the far east, and Hong Kong has been a big influence over the cyberpunk aesthetic so it was fitting to use it here. The words in the background are from a library reminder for loads of books I forgot to take back during my thesis, so they are all about cyberpunk. Frankenstein is the perfect symbol of so much of modernity, so he went in there. The hand is from a photo of Monet [EDIT: or was it Matisse? Ah well, the point was the same!] - which was picked for being a bit of a joke about the lack of classical materials in the picture - and the wings next to it are grafted on, making a visual chimera that works with the theme.
Aaaaand there's loads more stuff that I'm not going to write about at the moment because I fancy a cup of tea!
In general, I resist 'map art' because it's so often done by people at degree level, but I think that if it's there for a good reason then it's justified, but it can be easily over-used.