1 This is the Accepted Version of the article that was published in The Cartographic Jour- nal, 52:4 (2016), 318-324: http://www.tandfonline.com/doi/abs/10.1080/00087041.2015.1108657 How large was the Earth in the sixteenth century? The length of the degree of latitude in the Iberian Cartography of the Renaissance Joaquim Alves Gaspar Centro Interuniversitário de História das Ciências e da Tecnologia Faculty of Sciences – University of Lisbon alvesgaspar@netcabo.pt Abstract In this paper the results of a cartometric analysis of a number of Portuguese and Spanish charts of the sixteenth and seventeenth centuries are presented and conclusions are drawn concerning the length of the degree of latitude adopted in the Iberian nautical cartography of the Renaissance. Under the light of what we know about the navigational and charting meth- ods of the time, a new interpretation of the textual and cartographic sources is proposed. Ra- ther than being the result of technical considerations or precise measurements, the adoption of the various standards during this long period appears to be no more than the echoes of the traditional models of the Earth and of the political disputes between Portugal and Spain. Introduction When the systematic maritime exploration of the Atlantic started, during the first half of the fifteenth century, the shape and size of our planet was not an important subject. Although most educated people knew that the Earth was round, such knowledge was not relevant for the routine practice of navigation and chart making. Even after the rebirth of scientific cartography, following the translation and dissemination of Ptole- ŵLJs Geography, nautical charts continued to be constructed exactly as before, under the implicit assumption of a flat Earth. Not because the pilots and cartographers were ignorant about the real shape of our planet but due to the constraints imposed by the navigational methods of the time, which were based on magnetic directions and esti- mated distances. The introduction of astronomical navigation made things change, as pilots began to determine the latitude at sea and on land, and the incorporation of the new element