Determining the boundaries of Kurdistan is difficult; however, approximately, it comprises the north of Urmia and Van and their environs, and the banks of the Karkheh and Diyala rivers, and it extends to the sources of the Tigris. In its northwest the sources of the Tigris and Euphrates come together, and in the north it also encompasses the basin of the Aras River. Based on this information, in the Ottoman domains Kurdistan includes the Vilayet of Mosul and the areas along the Tigris, and the vilayets of Van, Bitlis, Diyarbakır, Dersim, and Mamuretülaziz. In Iran, Kurdistan also includes half of the Vilayet of Azerbayjan; accordingly, Azerbaijan forms the northeastern part of Kurdistan, ‘Iraq-i ‘Ajam its east, ‘Iraq al-‘Arab and Luristan its south, al-Jazira its southwest, and in the northwest it is bounded by Anatolia.