You upload the 120 pictures first. Then there is a predetemined allotment of available pics for 5 categories. 1 for each park and one for "beyond the parks" which includes an ability to choose your resort. Then YOU CHOOSE how you want to allocate any combination of your uploaded pictures, your photopass pictures or disney "stock" pictures into each of the spaces in each category. So, it makes sense for you to choose to move the pictures of your familiy in front of the castle into the Magic Kingdom section. But it does not have to. For example, I had a picture of my kids with Rafiki taken at MGM that I put in the AK section. It just fit better.
Now, someone mentioned that at the end of the DVD they include your 120 uploaded pictures. I did not read that anywhere on the photomovie site but just in case they do, I uploaded my pictures in the order I would want them to come out on a slide show...