LONDON IS BOTH the most explored and the most ungraspable of cities. As anyone who lives south of the river knows, not even black-cab drivers feel at home everywhere in the capital. It is hardly surprising, then, that London should always have been at the cutting edge of urban cartography. Two innovations, in particular, have inspired imitations around the world. The first, Phyllis Pearsall’s painstakingly traced street-plan, gave us the city from A to Z; the second, Harry Beck’s map of the Underground, recalibrated it. These twin peaks of the cartographer’s art are inspirations for any student of the capital, since London’s history – ‘a kaleidoscope of many stories rather than a book with one author or one theme’, as A N Wilson puts it – is just as unfathomable as the city’s streets. Two new books, in a wonderfully complementary manner, illustrate this perfectly. The first, Wilson’s, certainly makes no claims to being comprehensive (since its chief virtue is conciseness), but it is as clearly ordered as any pocket A-Z; the second, Stephen Smith’s Underground London, helps us to trace, like Beck’s map, the patterns of the city beneath the streets. Both impose order on the chaos that is London – but there all resemblances end.