▁( 1 3 0 4 – 1 3 6 8 ?) ▁wrote ▁" R ih lah " ▁( Tra vel s ) ▁based ▁on ▁three ▁dec ades ▁of ▁jour ne ys , ▁covering ▁more ▁than ▁ 1 2 0 , 0 0 0   km ▁through ▁northern ▁Africa , ▁southern ▁Europe , ▁and ▁much ▁of ▁Asia . ▁ ▁Regional ▁cart ography ▁Islam ic ▁regional ▁cart ography ▁is ▁usually ▁categor ized ▁into ▁three ▁groups : ▁that ▁produced ▁by ▁the ▁" B alk h ī ▁school ", ▁the ▁type ▁de vised ▁by ▁Muhammad ▁al - Id ris i , ▁and ▁the ▁type ▁that ▁are ▁uniqu ely ▁found in ▁the ▁Book ▁of ▁curios ities . ▁ ▁The ▁maps ▁by ▁the ▁B alk h ī ▁schools ▁were ▁defined ▁by ▁political , ▁not ▁longitud inal ▁boundaries ▁and ▁covered ▁only ▁the ▁Muslim ▁world . ▁In ▁these ▁maps ▁the ▁distances ▁between ▁various ▁" st ops " ▁( c ities ▁or ▁rivers ) ▁were ▁equal ized . ▁The ▁only ▁shapes ▁used ▁in ▁designs ▁were ▁vertical s , ▁hor izont als , ▁ 9 0 - deg ree ▁angles , ▁and ▁ar cs ▁of ▁circles ; ▁unnecessary ▁ge ographical ▁details ▁were ▁elimin ated . ▁This ▁approach ▁is ▁similar ▁to ▁that ▁used ▁in ▁sub way ▁maps , ▁most ▁notable ▁used ▁in ▁the ▁" Lond on ▁Under ground ▁T ube ▁Map " ▁in ▁ 1 9 3 1 ▁by ▁Harry ▁Beck . ▁ ▁Al - Id r ī s ī ▁defined ▁his ▁maps ▁differently . ▁He ▁considered ▁the ▁extent ▁of ▁the ▁known ▁world ▁to