Geography and cartography in the medieval Islamic world
Medieval Islamic geography and cartography were the study of geography and cartography in the Muslim world during the Islamic Golden Age. Muslim scholars made advances to the map-making traditions of earlier cultures, explorers and merchants learned in their travels across the Old World. 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.
History
8th and 9th 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. 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, 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. Thus his patronage resulted in the refinement of the definition of the Arabic mile 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.
Islamic cartographers inherited Ptolemy's Almagest and Geography in the 9th century. These works stimulated an interest in geography but were not slavishly followed. Instead, Arabian and Persian cartography followed Al-Khwārizmī in adopting a rectangular projection, shifting Ptolemy's Prime Meridian several degrees eastward, and modifying many of Ptolemy's geographical coordinates.
Having received Greek writings directly and without Latin intermediation, Arabian and Persian geographers made no use of T-O maps.
In the 9th century, the Persian mathematician and geographer, Habash al-Hasib al-Marwazi, employed spherical trigonometry and map projection methods in order to convert polar coordinates to a different coordinate system centred on a specific point on the sphere, in this the Qibla, the direction to Mecca. Abū Rayhān Bīrūnī later developed ideas which are seen as an anticipation of the polar coordinate system. Around 1025, he describes a polar equi-azimuthal equidistant projection of the celestial sphere. However, this type of projection had been used in ancient Egyptian star-maps and was not to be fully developed until the 15 and 16th centuries.
Khordadbeh–Jayhani tradition
The works of Ibn Khordadbeh and Jayhani were at the basis of a new Perso-Arab tradition in Persia and Central Asia. The exact relationship between the books of Khordadbeh and Jayhani is unknown, because the two books had the same title, have often been mixed up, and Jayhani's book has been lost, so that it can only be approximately reconstructed from the works of other authors who seem to have reused some of its contents. According to Vasily Bartold, Jayhani based his book primarily on the data he had collected himself, but also reused Khordadbeh's work to a considerable extent. Unlike the Balkhi school, geographers of the Khordadbeh–Jayhani tradition sought to describe the whole world as they knew it, including the lands, societies and cultures of non-Muslims. As vizier of the Samanid Empire, Jayhani's diplomatic correspondence allowed him to collect much valuable information from people in faraway lands. Nevertheless, Al-Masudi criticised Jayhani for overemphasising geological features of landscapes, stars and geometry, taxation systems, trade roads and stations allegedly few people used, while ignoring major population centres, provinces and military roads and forces.Balkhi school
The Balkhī school of terrestrial mapping, originated by Abu Zayd al-Balkhi in early 10th century Baghdad, and significantly developed by Istakhri, had a conservative and religious character: it was only interested in describing mamlakat al-Islām, which the school divided into 20 or more iqlīms. Balkhi and his followers reoriented geographic knowledge in order to bring it in line with certain concepts found in the Quran, emphasised the central importance of Mecca and Arabia, and ignored the non-Islamic world. This distinguished them from earlier geographers such as Ibn Khordadbeh and Al-Masudi, who described the whole world as they knew it.The geographers of this school, such as Istakhri, al-Muqaddasi and Ibn Hawqal, wrote extensively of the peoples, products, and customs of areas in the Muslim world, with little interest in the non-Muslim realms, and produced world atlases, each one featuring a world map and twenty regional maps.
Regional cartography
Islamic regional cartography is usually categorized into three groups: that produced by the "Balkhī school", the type devised by Muhammad al-Idrisi, and the type that are uniquely found in the Book of curiosities.The maps by the Balkhī schools were defined by political, not longitudinal boundaries and covered only the Muslim world. In these maps the distances between various "stops" were equalized. The only shapes used in designs were verticals, horizontals, 90-degree angles, and arcs of circles; unnecessary geographical details were eliminated. This approach is similar to that used in subway maps, most notable used in the "London Underground Tube Map" in 1931 by Harry Beck.
Al-Idrīsī defined his maps differently. He considered the extent of the known world to be 160° and had to symbolize 50 dogs in longitude and divided the region into ten parts, each 16° wide. In terms of latitude, he portioned the known world into seven 'climes', determined by the length of the longest day. In his maps, many dominant geographical features can be found.
''Book on the appearance of the Earth''
's was completed in 833. It is a revised and completed version of Ptolemy's Geography, consisting of a list of 2402 coordinates of cities and other geographical features following a general introduction.Al-Khwārizmī, Al-Ma'mun's most famous geographer, corrected Ptolemy's gross overestimate for the length of the Mediterranean Sea ; Ptolemy overestimated it at 63 degrees of longitude, while al-Khwarizmi almost correctly estimated it at nearly 50 degrees of longitude. Al-Ma'mun's geographers "also depicted the Atlantic and Indian Oceans as open bodies of water, not land-locked seas as Ptolemy had done. " Al-Khwarizmi thus set the Prime Meridian of the Old World at the eastern shore of the Mediterranean, 10–13 degrees to the east of Alexandria and 70 degrees to the west of Baghdad. Most medieval Muslim geographers continued to use al-Khwarizmi's prime meridian. Other prime meridians used were set by Abū Muhammad al-Hasan al-Hamdānī and Habash al-Hasib al-Marwazi at Ujjain, a centre of Indian astronomy, and by another anonymous writer at Basra.
Al-Biruni
devised a novel method of determining the Earth's radius by means of the observation of the height of a mountain. He carried it out at Nandana in Pind Dadan Khan. He used trigonometry to calculate the radius of the Earth using measurements of the height of a hill and measurement of the dip in the horizon from the top of that hill. His calculated radius for the Earth of 3928.77 miles was 2% higher than the actual mean radius of 3847.80 miles. His estimate was given as 12,803,337 cubits, so the accuracy of his estimate compared to the modern value depends on what conversion is used for cubits. The exact length of a cubit is not clear; with an 18-inch cubit his estimate would be 3,600 miles, whereas with a 22-inch cubit his estimate would be 4,200 miles. One significant problem with this approach is that Al-Biruni was not aware of atmospheric refraction and made no allowance for it. He used a dip angle of 34 arc minutes in his calculations, but refraction can typically alter the measured dip angle by about 1/6, making his calculation only accurate to within about 20% of the true value.In his Codex Masudicus, Al-Biruni theorized the existence of a landmass along the vast ocean between Asia and Europe, or what is today known as the Americas. He argued for its existence on the basis of his accurate estimations of the Earth's circumference and Afro-Eurasia's size, which he found spanned only two-fifths of the Earth's circumference, reasoning that the geological processes that gave rise to Eurasia must surely have given rise to lands in the vast ocean between Asia and Europe. He also theorized that at least some of the unknown landmass would lie within the known latitudes which humans could inhabit, and therefore would be inhabited.
''Tabula Rogeriana''
The Arab geographer Muhammad al-Idrisi produced his medieval atlas, Tabula Rogeriana or The Recreation for Him Who Wishes to Travel Through the Countries, in 1154. He incorporated the knowledge of Africa, the Indian Ocean and the Far East gathered by Arab merchants and explorers with the information inherited from the classical geographers to create the most accurate map of the world in pre-modern times. With funding from Roger II of Sicily, al-Idrisi drew on the knowledge collected at the University of Córdoba and paid draftsmen to make journeys and map their routes. The book describes the Earth as a sphere with a circumference of but maps it in 70 rectangular sections. Notable features include the correct dual sources of the Nile, the coast of Ghana and mentions of Norway. Climate zones were a chief organizational principle. A second and shortened copy from 1192 called Garden of Joys is known by scholars as the Little Idrisi.On the work of al-Idrisi, S. P. Scott commented:
Al-Idrisi's atlas, originally called the Nuzhat in Arabic, served as a major tool for Italian, Dutch and French mapmakers from the 16th century to the 18th century.