Ron,
I agree with what Pete was hinting at in his post about scale.
The idea of a backdrop is to provide a sense of distance...which means using forced perspective (objects farther away are modeled in reduced scale).
You have to differentiate between building flats or other reduced relief objects close to the tracks vs. the distant hills. Rarely can both be represented in the same way or with the same medium.
In other words, you most often need to superimpose nearby, close to 1:48 scale building flats or printed photos of buildings on top of a backdrop of distant objects in forced perspective.
This photo is a city scene, but the distant buildings on the backdrop could just as easily have been distant hills. The larger foreground buildings are separate photos pasted collage-style on the backdrop.
Creating the foreground flats separately from the distant backdrop also gives you a lot more freedom in how it all comes together, rather than trying to find a printed backdrop with all of these features in one shot.
Jim