Ptolemy's Geographia systematized the use of latitude, longitude, and projection methods to represent the known world. Although it contained significant errors — especially in the length of the Mediterranean and in conceiving the Indian Ocean as a closed sea — it fixed a model of mathematical cartography that influenced the Islamic world, Byzantium, and Renaissance Europe. Its role is foundational but not exclusive: the chain that starts here passes through Baghdad and Palermo before reaching Mercator.