Al-Idrīsī created a map of the world primarily through a combination of the following methods:
- He gathered information from explorers, traders, and travelers who had ventured to various regions. This allowed him to compile knowledge about different places and cultures.
- He studied existing geographic works and combined this knowledge with observations from various sources. He translated and adapted information from earlier maps and texts from different cultures, including the works of Ptolemy and Arab scholars.
Although al-Idrīsī did not specifically build an observatory for cartography, he did use scientific and mathematical principles in his work. His map, known as the "Tabula Rogeriana," was created in 1154 for King Roger II of Sicily and is renowned for its accuracy and detail at the time.
Out of the options you provided, the most relevant would be that he translated books from other languages, as this indicates his integration of existing knowledge into his cartographic efforts. However, it's crucial to recognize that he also relied heavily on information from explorers and firsthand accounts.