I am trying to draw a detailed dataflow diagram with a border representing the process I'm detailing; data stores outside the border are also used elsewhere, while those inside are not (Gane and Sarsen notation). In Photoshop Elements a lower layer is depicted behind a higher layer, so a shape can enclose other shapes without covering them. How can I do this here? I also tried "Send to back" with a rounded rectangle but it has no effect.

I figured out that a good strategy is to put the enclosing rounded rectangle in its own layer, and move this layer behind the default layer that contains the rest of the diagram. This way I can make the enclosure invisible with the eyeball layer tool when I'm working on the rest of the diagram. I have to keep track of which layer is the current one, or objects I draw disappear from view.

I read your instructions, but I have no idea of the actual use of a layer. I assume that you could use them in a variety of ways. For example, one could do a use case and then break down the bubbles into activity diagrams. However, I don't know how best to use layers to create workable code. An example would be very useful.

I had the impression it was a way of nesting lower levels. If I'm doing an activity diagram where each Activity represents the roll up of lower level activities, do I handle the lower levels as separate projects rather than layers?

Thanks. That's exactly what I was looking for.