I contacted one of the larger on-line model railroad stores and asked what did they have that would fit a 20’ wide wall with a backdrop. They have on line a number of backdrops but at the scale they show it is hard to figure which would abut each other, also if they could not fit a 20’ could they fit a 12’ width and another at 8’ wide with similar backdrops, I could always build a mountain between the two.
Backdrops are measured from the bottom up, and they need to be as tall as they need to be to hide whatever you do not want people to see.
They are as long as your layout, or as long as whatever part of the layout you want it to cover.
HERE is a backdrop on a 1:1 scale layout in Brooklyn [(-D]
Here is one of my trains on the Smith-9th Street viaduct. I panned several shots from the train platform, stitched them together with panoramic software on my computer and pasted them to a structural member on the middle level of my layout.
Toward the top of the picture you can see the shadow cast by the level above this one. Here is a photo of the Brooklyn skyline from the same platform… On my layout as on the real photo, much of the skyline is below the horizon of the picture because the elevated structure is so tall. On my layout a person standing close to the station will see that detail below the platform view of the above shot.
Sorry, I find your post confusing. First you are talking about running length, then you shift to width. You refer to 20’ and then to 20"
Do you mean height? Perhaps the retailer became confused in the same way. Some commercial backdrop companies refer to the height of the backdrop as “width”, since that’s the way it comes off the roll printer.
There are multiple vendors who provide much longer backdrops than 36", even up to 200 feet continuous runs.
Backdrop Warehouse
(confusing website, but they provide continuous lengths up to 200 feet, it appears)
Backdrop Junction
(I know that a client has purchased a backdrop from them that is around 180". I don’t know if that was a custom job)
From Backdrop Warehouse - We saw a few refers from this post. We have unlimited horizontal length same scene or transitions or reversals and vertical 12" to 80". All are custom size, scale, resolution, except low end cost preprinted starting at $9. Call if questions and we will try to help.