Something I often do when reviewing a book is talk about it in terms of the expectations of its potential readers—particularly if readers might come to a book with expectations that the book does not meet, because the book is doing something different. If you’re expecting The Eternal City: A History of Rome in Maps, written by the art historian Jessica Maier and published last November by the University of Chicago Press, to be basically A History of Rome in 100 Maps, it isn’t: the count is more like three dozen. This doesn’t mean that The Eternal City is a slight book—it most certainly is not, though at 199 pages it’s a bit shorter than, say, A History of America in 100 Maps (272 pages).
But counting maps would miss the difference in Maier’s approach. To invoke xkcd, this is depth-first rather than breadth-first: there are fewer maps here, but they’re discussed in much more depth than the two-page spreads of the hundred-map books, and provided with much more context. This is a history of Rome in maps in which history, Rome and maps all get their proper share of attention.