I really thought this was simple but it's been giving me some grief as late, so maybe I'm missing something obvious.
I'd like to create a scrolling animation that retains a consistent background as the camera pans over the animation. So I've created a 12,000 x 1080 comp (for example) and would like a build a landscape that covers the entire comp. However, as soon as I add in a camera, the camera is set to view the whole 12,000 width rather than just a regular 1920 x 1080 view.
Think of your comp as the camera viewfinder. You can make your landscape much larger than what you see in the viewfinder. So your comp should be 1920x1080 but you can keep your landscape 12,000 pixels wide.