Geography and cartography in the medieval Islamic world

Medieval Islamic geography and cartography refer to the study of geography and cartography in the Muslim world during the Islamic Golden Age (variously dated between the 8th century and 16th century). Muslim scholars made advances to the map-making traditions of earlier cultures, particularly the Hellenistic geographers Ptolemy and Marinus of Tyre, combined with what explorers and merchants learned in their travels across the Old World (Afro-Eurasia). Islamic geography had three major fields: exploration and navigation, physical geography, and cartography and mathematical geography. Islamic geography reached its apex with Muhammad al-Idrisi in the 12th century. Islamic geography began in the 8th century, influenced by Hellenistic geography, combined with what explorers and merchants learned in their travels across the Old World (Afro-Eurasia). Muslim scholars engaged in extensive exploration and navigation during the 9th-12th centuries, including journeys across the Muslim world, in addition to regions such as China, Southeast Asia and Southern Africa. Various Islamic scholars contributed to the development of geography and cartography, with the most notable including Al-Khwārizmī, Abū Zayd al-Balkhī (founder of the "Balkhi school"), Al-Masudi, Abu Rayhan Biruni and Muhammad al-Idrisi. Islamic geography was patronized by the Abbasid caliphs of Baghdad. An important influence in the development of cartography was the patronage of the Abbasid caliph al-Ma'mun, who reigned from 813 to 833. He commissioned several geographers to perform an arc measurement, determining the distance on earth that corresponds to one degree of latitude along a meridian (al-Ma'mun's arc measurement). Thus his patronage resulted in the refinement of the definition of the Arabic mile (mīl in Arabic) in comparison to the stadion used in the Hellenistic world. These efforts also enabled Muslims to calculate the circumference of the earth. Al-Mamun also commanded the production of a large map of the world, which has not survived, though it is known that its map projection type was based on Marinus of Tyre rather than Ptolemy.