He conceived the celestial sphere by using only latitude and longitude; however, he imagined that the ecumene extended from the Canaries to China for 225°, an excessively exaggerated extent, and his map, constructed on a grid of straight parallels and meridians according to an equidistant cylindrical projection and without taking into account the convergence of meridians toward the pole, presented maximum distortions in the peripheral zones. P. sought to reduce the errors of MARINUS OF TYRE, but while he remained essentially tied to his predecessor’s system both in the Almagest and in the Μαθηματική συνταξίες τετράβιβλος, a supplement to the former, and in his minor astronomical works, he demonstrated original conceptions in the more properly geographical field and particularly in cartography by compiling the Γεωγραφική ὀργήγησις. He reduced the extent of the ecumene to 180°, approaching the actual 125°; he adopted the cylindrical projection only to represent small portions of the earth’s surface (chorographical maps); he proposed a simple conical projection in which the meridians are straight lines converging toward the poles and the parallels are concentric arcs of circles, and on this basis he constructed or at least provided the basis for constructing a general map of the known world, including all the territory from north to south between Thule and Agisymba, and from east to west from the Canary Islands (Fortunae) and Sera Metropolis, capital of the country of the Seres (China). Scholars debate whether the 27 maps (one general and the others regional) inserted in the medieval manuscripts of his work (most importantly the Vatican Greek 82, in the Apostolic Vatican Library, of the 12th century) derive directly from P., albeit with inevitable distortions in the development of the tradition, or were instead constructed later based on P.’s text, which, moreover, consisted essentially of a long list of localities with their respective latitude and longitude and was particularly susceptible to corruption.
The erroneous value in the measurement of the greatest circumference of the earth, at 180,000 stades (ca. 32,000 km, significantly less than the true 40,070 km), which persisted into the Middle Ages, also influenced the calculations of Christopher Columbus and the discovery of the New World. Transmitted to later cartography, especially Arabic, other errors of P.’s endured, such as the exaggerated east-west stretching of the Mediterranean Sea, the orientation of the Italian peninsula, and the closure of the Indian Ocean south of Zanzibar, where the coastline is depicted as turning sharply eastward.
While P.’s astronomical work, disseminated especially through the Arabs, remained at the foundation of all medieval cosmography and Scholastic philosophy, his geographical work enjoyed little success, especially in the West, where only in the 15th century did a first Latin translation in 1409 mark the beginning of a new era in the history of cartography.
P. also wrote on chronology, mechanics, optics, music, etc.