GB, As Karl mentioned, the ceder strips are tongue and grooved. I glued together three strips, and added two 1 1/4" ceder cleats on the back for strength. The portrait is then glued to the top. I guess you can call the ceder a backing board.
Sheila, The advantage to stack cutting is you have more than one project and it gives better support when cutting. I never like to cut anything thinner than 1/4". So if I needed one piece that was 1/8", I would laminate it to a piece of cheap plywood, and throw away the plywood when done. But since I am doing two shows this year, I am building stock in stack cutting.