Stacked Layers was a new technique introduced in Vectorworks 2008. Before Vectorworks 2008, if you wanted to see a complete view of your project, you would make a new layer for 3D viewing. Then you could layer link all your design layers to the 3D model layer. With Vectorworks 2008 and 2009, you do not have to set up the 3D model layer. Stacked Layers allow you to see all the visible layers in your file, and when you move the view around, all the layers look like they are joined together.