Ptolemy's Geography (or more literally, Geographical Guide, Γεωγραφικὴ Ὑφήγησις) has a special status within the Graeco-Roman tradition of writings relating to the construction of maps of the known world. The principal earlier works, by Eratosthenes, Hipparchos and Marinos of Tyre, are lost but partially known through substantial references in Strabo and Ptolemy. They were discursive commentaries on the world map (conceived as a visualisation of the current and hence evolving understanding of the spatial relations between localities) consisting largely of critical discussion of the available evidence and of ways in which earlier writers had used or abused it. Ptolemy gives us very little of that kind. He accepts the voluminous and chaotic writings of Marinos (first decades of the second century ce, about half a century before Ptolemy composed the Geography) as the best immediate basis for the geographical contents of a world map, limiting his own contributions on this topic chiefly to a systematic compression of the southernmost and easternmost parts of Marinos’ map to obtain a more reasonable estimate of the latitudinal and longitudinal extent of the known world, a resolution of conflicts in Marinos’ data, and corrections and updatings that mostly pertain to the Indian Ocean and the lands bordering it, drawing on recent sources that he does not discuss or even identify. Ptolemy's contributions to the cartographic project are, firstly, advocacy of a cartographic method depending for all the macroscopic features of the map on astronomically measured latitudes and longitudes; secondly, prescribing sophisticated, mathematically defined constructions of grids of parallels and meridians for a planar world map to preserve approximately the proportions of distances between places on the terrestrial globe; and, thirdly, the complete digitisation of the world map in the form of ordered lists of localities with their longitudes and latitudes in degrees and fractions of a degree so that maps of the entire known world or of smaller regions can be constructed precisely from this textual-numerical representation, thus avoiding the distortions that arise in copying an image visually from an image.

The focus of R.'s monograph is on the geographical content of the Geography, that is, the aspects that are largely (though not entirely) based on Marinos as filtered through Ptolemy's reworking. This material is mostly comprised in the lists of localities in Books 2–7, supplemented by parts of Ptolemy's critique of Marinos in Book 1. Following an introduction that succinctly summarises the broader history of Graeco-Roman cartography and a first chapter situating the Geography in Ptolemy's scientific career and oeuvre, the remainder of the book is a kind of reader's guide to the Geography, proceeding through its contents chapter-by-chapter. For the list of localities, the approach is not simply to provide a verbal synopsis, though this is useful for the student of the Geography since Ptolemy's dry tabular format does not easily convey a connected idea of the region under consideration until one plots the data in the form of a map. R. also illuminates Ptolemy's toponyms, ethnonyms and spatial information in the light of each region's ancient history and ethnography, while pointing out errors, inaccuracies and idiosyncrasies in the nomenclature as well as in the positional data. The Geography has not received a comprehensive treatment of this kind before, and this will be a valuable guide for scholars who wish to explore the treatise as a historical and geographical source. Line-drawing maps representing the data in the Geography are provided for each region. These are based (this does not seem to be explicitly acknowledged) on the reconstructed maps in the 2006 Stückelberger–Graßhoff critical edition. Their usefulness is diminished, however, by the omission of local features such as city names, ethnonyms and physical features; all they show are the coastlines, the borderlines of the ‘provinces and satrapies’ into which Ptolemy subdivides each continent, and rivers.

R. broadly adheres to the Stückelberger–Graßhoff edition except for the toponyms (the handling of which he characterises as ‘erratic’), and he engages little with the ‘complex and contradictory’ manuscript tradition (p. 23). For the most part this policy is fine for his purposes, but sometimes it would be helpful for readers to be made aware of divergences among the manuscripts, especially since the manuscripts that Stückelberger–Graßhoff chiefly follow represent a recension in which Byzantine editorial intervention is frequently in evidence, for example longitudes and latitudes arbitrarily modified where corrupted numerals would have caused coastlines to cross themselves, islands to be situated inland or cities to be in the sea. A noteworthy instance where attention to the manuscripts would have been constructive is the location of the westernmost meridian of Ptolemy's known world, which Ptolemy consistently calls the meridian ‘through the Blessed Islands’ (scil. the Canaries). R. (p. 18) is troubled by the fact that in Geog. 4.6 the six Blessed Islands are all assigned longitudes 1° east of the westernmost meridian, forming a straight north–south row while the limiting meridian apparently passes through no land at all. But in the sole extant manuscript (Vat. gr. 191) that has a text independent of the Byzantine recension four of the islands have a longitude of 0°, notated using the Greek zero symbol that was part of the sexagesimal notation prevalent in mathematical astronomy. These zeros are surely authentic Ptolemy, and they were later replaced by alphas, either because a medieval copyist did not recognise what they were or to avoid having to draw islands right on the edge of the map.

The mathematical aspects of the Geography are treated more cursorily, and there are a few mistakes and misunderstandings. R. asserts (p. 15) that the terminology of ‘latitude’ and ‘longitude’ (literally ‘length’ and ‘breadth’, μῆκος and πλάτος) was not applied in a geographical sense in antiquity. In fact Ptolemy uses them in the Geography (e.g. 1.19 ἐποχάς … κατὰ μὲν τὸ μῆκος, … κατὰ δὲ τὸ πλάτος, ‘positions … in longitude … and in latitude’, and 2.1 μοιρογραφίας μήκους τε καὶ πλάτους, ‘recorded degrees of longitude and latitude’); he may have introduced this terminology on the analogy of their astronomical employment for ecliptic coordinates on the celestial sphere. R.'s statement (p. 19) that Ptolemy ‘stressed … that he would make the meridians parallel’ when drawing a map apparently refers to 8.1, where the maps in question are the regional maps that cover a comparatively small latitudinal extent, but for a world map Ptolemy considered a rectangular grid of meridians and parallels unacceptable, castigating Marinos in 1.20 for having prescribed such a format. Commenting on 7.6, R. (p. 180) explains κρικωτὴ σφαῖρα as ‘a spherical depiction of the earth with latitude and longitude lines on it’. Rather, it means an armillary sphere whose rings represent the principal celestial circles, and the chapter describes how to construct a picture of a terrestrial globe, bearing a map of the known world, inside an armillary. An example of such an image surviving from antiquity (though lacking an actual map) is the mosaic from the House of Leda at Soluntum. Lastly, while R. correctly understands the ὑπογραφαί of the regional maps in 8.2–28 as captions for the maps (an explanation first offered in the 2000 Berggren–Jones translation), he does not note that 7.5 and 7.7 are also ὑπογραφαί in this sense, captions for the world map and for the picture of the globe inside the armillary.

These reservations aside, R.'s book can be warmly recommended as a gateway to the most detailed and extensive document of spatial geographical knowledge that has survived from Graeco-Roman antiquity.