Most Arab cartographers used Ptolemy's instructions in the construction of their own maps. With this basis the Moslems combined the accumulated knowledge gained through exploration and travel. Moslem trade between the 7th and 9th centuries reached China by sea and by land; southward it tapped the more distant coasts of Africa, including Zanzibar; northward it penetrated Russia; and westward Mohammedan navigators saw the unknown and dreaded waters of the Atlantic. Their own enlarged knowledge of the explored-world helped to broaden their cartographic outlook, and the preeminence of their civilization was soon acknowledged by contemporaries.

In the 11th century the Norman conquerors were beginning their advance westward and southward, overrunning the littoral of Western Europe, reaching the Mediterranean and establishing themselves in Southern Italy between 1066 and 1071. These new rulers preserved much of what was best of this Arabic tradition and culture, and Moslem scholars played a brilliant part in the intellectual life of the court. The Norman king was Roger II Guiscard of Sicily (1097-1154) who was active in encouraging science and learning of all areas, but was himself a devotee of geography, occupying much of his spare time in collecting Arabic geographical treatises and in questioning travelers about distant lands. Palermo was one of the great meeting places for sailors, merchants, pilgrims, crusaders, and scholars from all nations. Their accounts of distant lands could be heard, and it is not surprising that at the court of King Roger the idea was conceived of compiling a book and a map from all of these diverse reports.

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It was, therefore, at Roger's instigation and patronage that Abu Abdullah Ibn Idrisi (born 1099 at Ceuta) was summoned to his court to collaborate with him in the compilation of a book containing all available data on the latitude and longitude of towns, the distances between them, and their distribution in climate zones. Furthermore, we are told that Roger provided Idrisi with special facilities for the construction of maps to accompany the resulting treatise, usually known as his Geography, or, to cite the translation of its Arabic title, The Recreation for Him Who Wishes to Travel Through the Countries. Idrisi was much traveled himself and, unlike many other Arabs of his time, had been to France and England as well as Central Asia and Constantinople. Also, as a student at the University of Cordova, he had access to the rich repository of information on various countries collected there.

In addition to Idrisi's personal travel and scholarship, it appears that the king and Idrisi together selected "certain intelligent men", who were despatched on travels and were accompanied by draftsmen. Just as soon as these men returned Idrisi inserted in his treatise the information which was thus communicated to him. Therefore, on the basis of these observations made 'in the field', and from data derived from such sources as Ptolemy and earlier Arabic and Greek geographers, geographical information was critically compiled, correlated, and brought up to date. The resulting book and associated maps took 15 years to amass and are, for this and the above reasons, unquestionably among the most interesting monuments of Arabian geography. In addition, the book is the most voluminous and detailed geographical work written during the 12th century in Europe.

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The plan of this treatise is simple, though somewhat artificial. After a brief description of the earth as a globe, which he computed to be 22,900 miles in circumference and judged to remain stable in space like the yolk in an egg, and of the hemispheres, climates, seas and gulfs, Idrisi launches into a long and detailed account of the regions of the earth's surface. He takes up the seven climates in order, dividing each climate into ten longitudinal sections, an artificial arrangement started earlier by Islamic astronomers. These seventy sections are described minutely, illustrating each section with a separate map. When put together, these maps constitute a rectangular world map similar to the Ptolemaic design.

Idrisi fused elements from East and West with Arab knowledge to produce a world-picture. He was critical of traditional sources (even though he squeezed his map into a climate-zone framework) and he gathered much of the data for his map not only from contemporary lore and explorers' reports, but also from charts or from books of sailing instructions the Greeks called Periploi (these charts dated back to a mariner named Scylax, who kept a periplus, or record, of his voyage around the Mediterranean in about 350 B.C.). Idrisi's map of 1154 took the form of a silver tablet, probably measuring 3.5 X 1.5 meters (12 X 5 feet); later, in 1160, this tablet fell into the hands of a mob and was smashed to pieces. In 1154, a few weeks before Roger's death, manuscripts of the book in Latin and Arabic were completed, together with the rectangular map, which was drawn on 70 sheets, along with a small circular world map.

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