This paper explores the authorship of the anonymous La Carta del Cantino through an analysis of design signatures. Using high resolution digital copies of charts in ArcGIS, La Carta del Cantino is compared to contemporaneous charts. The long-held assumption that La Carta del Cantino was a surreptitious copy of the Portuguese king’s royal pattern chart is rejected in favor of a more simple explanation: Alberto Cantino commissioned the world chart from a chartmaker in Lisbon, and that chartmaker was Pedro Reinel.