In the north are part of the central Zagros Mountains; and in the south, a coastal plain, the largest in Iran. Eastern Khuzestan and Lorestan include part of the Tigris-Euphrates River system. The Shatt al-'Arab(3) forms a bit of Khuzestan's western border and the Karun joins it. Further north the Karkheh is the important system; it flows toward Iraq, but ends in marshland without reaching the Tigris. Its middle course forms one of the parallel valleys characteristic of this section of the Zagros. These mounains reach over 4,300 meters at Oshtoran Peak(4) in eastern Lorestan.
More than ten million people live here but no single first language is spoken by a majority.(5) Exact figures are hard to determine but more than one third of the people speak dialects of Kurdish, about one third dialects of Luri, perhaps one in ten speak Persian(6), nearly that many speak Mesopotamian spoken Arabic, and maybe more than one in twenty speak Domari(7).
Almost everyone is a Moslem. The Persians, Luri and Arabs are Shi'ite, the Kurds Sunni.
No city has a million residents, and no one of the provinicial capitals is predominant.
Iranian speakers entered the area from the east side of the Zagros in the first millenium B.C.E. The ones in Fars spoke Old Persian, the ancester of modern Persian. However, most elite tasks were done using Aramaic, a Semitic language. Later Aramaic largely gave way to Hellenistic Greek, and then to Parthian, the first Iranian adminstrative language. After Greek rule ended, Old Persian evolved into Middle Persian, also called Pehleve or Pazand, especially under the influence of Arabic. This influence became more manifest in the modern Persian of the last few centuries. Luria and Kurdish are also Iranian languages.
The Domari were one of three migrations out of India of Indo-Aryan groups, collectively known as gypsies by English-speakers, though this term has fallen into disfavor.
The Arabs that brought Islam were an elite in most of this area, but near the shared mouth of the Tigris-Euphrates they became a local and permanent majority.
north
east of Hamadan, and northeast of Lorestan
east of Lorestan
east and southeast of Khuzestan
south
southwest of Khuzestan, Ilam and Kermanshah Provinces, and northwest of Kermanshah Province
(1) Formerly Persia.
(2) Formerly Bakhtaran.
(3) Shatt al-'Arab is transliterated Arabic. It translates as Arab River-mouth.
(4) Peak is 'kuh' in transliterated Persian.
(5) The three Iranian languages of Persian, Luri and Kurdish together constitute a majority.
(6) Also called Farsi or Parsi.
(7) Estimates vary more than magnitudinally on the number of Domari speakers; I used the high estimate and guessed that half of Iran's total was local to this area.