There are several few visual allusions, that is I copied a lot of stuff including: Hieronymus Bosch, William Blake, Martin Wells Knapp, as well as the covers of Cosmographical Glasses and The Hobbit. For more influences, see my Scrapbook.
I was disappointed not to come up with a clear metaphor for separating representation from interaction. After publication, Phil Hawksworth suggested a vending machine with XML, HTML, JSON, etc radio buttons, which would have worked nicely. I also spent far too much energy exploring the dark side, in particular faux Web technologies and the dangers of outsourcing your strategy to purveyors of closed source lock-in. What I am proud of is the way progress comes from a series of places rather than actions, that is nouns, not verbs. Thus the drawing is itself quite RESTful!