A different clarification but about one BG rule that says you cannot:
use an image which is created in such a way that focusing on segments effectively changes scenes
Which I think is about basically having multiple discrete BGs on one image. I had an idea for the BG basically being a map that the screen pans around. I believe that's in the spirit of this rule saying you can:
reveal previously obscured information or areas through pans, zooms and cuts
But just confirming! As a back up I could always just have a fixed view of the map that reveals more locations over time if that's more in the spirit anyway.