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 (
Afro-Eurasia). 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 (particularly gazetteers) 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 (973–1048) 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 ( 870) and
Jayhani ( 910s) 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 (mostly from the eastern parts of the Islamic world) 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 (from
Balkh) 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 ("Islamic lands"), which the school divided into 20 or more
iqlīms ("climes" or provinces). 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, Al-Khwārizmī,
Al-Ma'mun's most famous geographer, corrected Ptolemy's gross overestimate for the length of the
Mediterranean Sea 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 (the prime meridian previously set by Ptolemy) and 70 degrees to the west of
Baghdad. Most medieval Muslim geographers continued to use al-Khwarizmi's prime meridian. 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 (1037), 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 (1097–1154), 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:
Piri Reis map The
Piri Reis map is a
world map compiled in 1513 by the
Ottoman admiral and cartographer
Piri Reis. Approximately one third of the map survives; it shows the western coasts of
Europe and
North Africa and the coast of
Brazil with reasonable accuracy. Various Atlantic islands, including the
Azores and
Canary Islands, are depicted, as is the mythical island of
Antillia and possibly
Japan.
Others Suhrāb, a late 10th-century Muslim geographer, accompanied a book of geographical
coordinates with instructions for making a rectangular world map, with
equirectangular projection or cylindrical equidistant projection. where he illuminated the cities and places of the
Turkic peoples of
Central and
Inner Asia. He showed the lake
Issyk-Kul (in nowadays
Kyrgyzstan) as the centre of the world.
Ibn Battuta (1304–1368?) wrote "Rihlah" (Travels) based on three decades of journeys, covering more than 120,000 km through northern Africa, southern Europe, and much of Asia.
Muslim astronomers and geographers were aware of
magnetic declination by the 15th century, when the Egyptian astronomer
'Abd al-'Aziz al-Wafa'i (d. 1469/1471) measured it as 7 degrees from
Cairo. == Instruments ==