The following map from the Institute for the Study of War, an American think tank, shows with black lines ISIS presence in Iraq (8th February 2016). By ISIS I mean the Sunni Islamists of Iraq i.e. the Sunni ex-socialists of Saddam Hussein. There are exceptions of course to this rule. See “Saddam Hussein: The Father of ISIS in Iraq”.
Map 1 Iraq (8th February 2016)
With the black lines you can see the areas controlled by ISIS, and as you can see ISIS controls the rich in oil Mosul in Northern Iraq. With orange and purple you can see the areas controlled by the Kurds of Iraq i.e. the rich in oil Kirkuk and Erbil (see red arrows on the map).
With green and yellow you can see the areas controlled by the majority of the Iraqi population i.e. the Shiite Arabs that came to power when the United States overturn the socialist Sunni dictator Saddam Hussein. The Shiite Arabs of Iraq control the rich in oil regions near Baghdad (Central Iraq) and also the rich in oil regions at the South, near the Persian Gulf.
At the following map from the Energy Information Administration you can see with gray blots the Iraqi oil and gas reserves. The rich in oil areas are at the south, near the Iranian-Iraqi borders, at Central Iraq, near Baghdad, and at Northern Iraq i.e. Mosul, Kirkuk, Erbil etc. With green and red you can see the oil networks of Iraq, which mainly end to Turkey at the north and the Persian Gulf at the south.
Map 2 Oil and Gas Fields of Iraq (EIA)
At the following map from Washington Post you can see that the Western Part of Iraq is a desert, and at the north there are the mountains of Iraqi Kurdistan, where the Turkish Kurds of PKK are hiding when the Turkish army is after them. Note that PKK has carried out many terrorist attacks in Turkey, asking for greater autonomy for the Kurdistan in Turkey. Sometimes in the past the Turks had the blessings of Saddam Hussein when they entered Iraqi Kurdistan to chase the Kurds, because the Kurds were a common enemy.
Map 3 The Iraqi Desert, the Iraqi Mountains and Mesopotamia
As you can see at the following map of Syria, from the New York Review of Books, the Syrian desert at South Syria is adjacent to the Iraqi desert at Western Iraq. Geography and natural barriers are important both for the construction of pipeline networks, but also for the supplies of the fighters.
Map 4 Map of Syria
I must also say that in Iraq, the United States, together with Iran, they support the Shiite Arabs at the South, and the United States also support the Kurds at the North. The Turks and the Arabs of the Persian Gulf support the Sunni Islamists of Iraq, but they are also trying to approach the Shiite Arabs in order to reduce the Iranian influence. The Turks have also common interests with the Kurds of Iraqi Kurdistan, because the Iraqi Kurds need to export their oil and the Turks need that oil. However the Turks are fighting the Kurds of Syria and Turkey. The Shiite Arabs of Iraq have problematic relations with the Kurds of Iraq, because the Iraqi Kurds do not pay commissions to the Shiite government of Baghdad from their oil exports. However the Shiite Arabs of Iraq and the Iraqi Kurds face ISIS as a common enemy.
“Iraq Control of Terrain Map: February 9, 2016”, February 2016