You are right:I’m pretty sure it’s cotton plantations or cotton production during the King Cotton era pre-Civil War
In defense of my honor, I saw a very similar map at the National African American History and Culture Museum in DC a few weeks ago.(Not saying that Truthy cheated in this specific case of course)
Be careful of posting maps you can easily find using the "search this imagen on Google" or "ask Cortana about this image" function in some browsers. I knew the correct answer a second after it was posted and didn't even notice it was a map of southern USA.
(Not saying that Truthy cheated in this specific case of course)
Ok, then: how radioactive various parts of the United States are.