▁" also ▁dep icted ▁the ▁Atlantic ▁and ▁Indian ▁O ce ans ▁as ▁open ▁bodies ▁of ▁water , ▁not ▁land - locked ▁se as ▁as ▁P to le my ▁had ▁done . ▁" ▁Al - K h war iz mi ▁thus ▁set ▁the ▁Prime ▁Mer id ian ▁of ▁the ▁Old ▁World ▁at ▁the ▁eastern ▁shore ▁of ▁the ▁Mediter rane an , ▁ 1 0 – 1 3 ▁degrees ▁to ▁the ▁east ▁of ▁Alexand ria ▁( the ▁prime ▁mer id ian ▁previously ▁set ▁by ▁P to le my ) ▁and ▁ 7 0 ▁degrees ▁to ▁the ▁west ▁of ▁Bag hd ad . ▁Most ▁medieval ▁Muslim ▁ge ograph ers ▁continued ▁to ▁use ▁al - K h war iz mi ' s ▁prime ▁mer id ian . ▁Other ▁prime ▁mer id ians ▁used ▁were ▁set ▁by ▁Ab ū ▁Muhammad ▁al - Has an ▁al - H amd ā n ī ▁and ▁Hab ash ▁al - Has ib ▁al - Mar w azi ▁at ▁U j j ain , ▁a ▁centre ▁of ▁Indian ▁astronom y , ▁and ▁by ▁another ▁anonymous ▁writer ▁at ▁Bas ra . ▁ ▁Al - B ir uni ▁Ab u ▁Ray han ▁al - B ir uni ▁( 9 7 3 – 1 0 4 8 ) ▁gave ▁an ▁estimate ▁of ▁ 6 , 3 3 9 . 6   km ▁for ▁the ▁Earth ▁radius , ▁which ▁is ▁only ▁ 1 7 . 1 5   km ▁less ▁than ▁the ▁modern ▁value ▁of ▁ 6 , 3 5 6 . 7 5 2 3 1