Good spot fireseed!
My guess is that it's smoke from a volcano, possibly? And using the smoke as a main mark, we can see how big the map will be.
(Sorry for the size differences)
A you can see in the (favourited by many) first wallpaper was taken faily close to the smoke, whereas the new wallpaper s very far away.
[IMG]http://i.imgur.com/A0F2a.jpg[/IG]
[IMG]http://i.imgur.com/7TQuX.png[/IG]
In the first picture I'm guessing that the new picture was taken far over to the left, over the mountain, where the yellow arrow stops.
And judging from the new picture, the first picture was taken far over to the right, over the furthest-right mountain. Sorry, the yellow arrow in the second image was supposed to be pointing over, past the mountain, but it slightly overlapped it.
