Here is a link to Mytholon’s Concept Art/Mattepainting post
http://www.zbrushcentral.com/zbc/showthread.php?t=32285&page=2&pp=15
The ideal is to have a point ( a vanishing point) on a layer with lines leading to the point (converging onto the point) but the point can be moved in any direction.
Here is a screen capture of the some of Mytholon’s image that shows the point and lines.