The maps structure works well for this kind of content: good for browsing at your leisure or looking up a specific location, and very well suited to a multi-touch tablet. Here's a video showing how it works (and there's also an official trailer): There's a separate top-down street-map with its own index, which is ideal for looking up roads mentioned in a particular book, and n mock-tourist style, there are also 'walking tours' taking you on themed jaunts around the living map, narrated by actress and comedian Helen Atkinson-Wood. Major locations like the Unseen University have text, quotes and artwork to provide more info, taken from print book The Compleat Ankh-Morpork. You pinch to zoom in and out of the map, tapping on little icons that appear on individual buildings to find out more about them. It attempts to create a 'living breathing map' of Pratchett's famous city, complete with strolling characters, chuffing chimneys and a soundtrack that ebbs and flows as you explore. The app costs £9.99 on Apple's App Store, and is iPad-only for now, requiring iOS 6.0 or later. Fail to match up, and everyone will know about it.

Why? Discworld has millions of fans of all ages, so there's bound to be lots of interest – but also high expectations based on each and every fan's mental picture of Ankh-Morpork. Discworld: The Ankh-Morpork Map is the work of publisher Transworld and app developer Agant, and it faces quite a challenge. Now in 2013 there's an iPad app trying to map it out.

The city felt real and living to me in a way that Tolkien's Middle-earth never did. The more books I read, the clearer a picture I had in my head about what Ankh-Morpork was like through Pratchett's descriptions and the cover artwork by Josh Kirby.

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