▁be ▁ 1 6 0 ° ▁in ▁longitude , ▁and ▁divided ▁the ▁region ▁into ▁ten ▁parts , ▁each ▁ 1 6 ° ▁wide . ▁In ▁terms ▁of ▁latitude , ▁he ▁portion ed ▁the ▁known ▁world ▁into ▁seven ▁' cl imes ', ▁determined ▁by ▁the ▁length ▁of ▁the ▁longest ▁day . ▁In ▁his ▁maps , ▁many ▁dominant ▁ge ographical ▁features ▁can ▁be ▁found . ▁ ▁Book ▁on ▁the ▁appearance ▁of ▁the ▁Earth ▁Muhammad ▁ibn ▁M ū s ā ▁al - K hw ā riz m ī ' s ▁ ▁(" Book ▁on ▁the ▁appearance ▁of ▁the ▁Earth ") ▁was ▁completed ▁in ▁ 8 3 3 . ▁It ▁is ▁a ▁re vised ▁and ▁completed ▁version ▁of ▁P to le my ' s ▁Geography , ▁consisting ▁of ▁a ▁list ▁of ▁ 2 4 0 2 ▁coordinates ▁of ▁cities ▁and ▁other ▁ge ographical ▁features ▁following ▁a ▁general ▁introduction . ▁ ▁Al - K hw ā riz m ī , ▁Al - Ma ' mun ' s ▁most ▁famous ▁ge ograph er , ▁corrected ▁P to le my ' s ▁gross ▁over est imate ▁for ▁the ▁length ▁of ▁the ▁Mediter rane an ▁Sea ▁( from ▁the ▁Can ary ▁Islands ▁to ▁the ▁eastern ▁sh ores ▁of ▁the ▁Mediter rane an ); ▁P to le my ▁over est im ated ▁it ▁at ▁ 6 3 ▁degrees ▁of ▁longitude , ▁while ▁al - K h war iz mi ▁almost ▁correctly ▁estimated ▁it ▁at ▁nearly ▁ 5 0 ▁degrees ▁of ▁longitude . ▁Al - Ma ' mun ' s ▁ge ograph ers