There are a few things about Aperture's Projects pane that can be confusing to new users. What's great about the Projects pane is that it provides so many options for keeping even a massive library organized. The combination of Projects, Folders, and Smart Albums provides tremendous organizational flexibility and power. However, there are a couple of things about the visual presentation of the Projects pane that can be confusing.

1. The Library entry in the Projects pane does not contain any images or projects. While it appears that the Library entry a the top of the Projects pane has a hierarchical relationship to the rest of the entries in the pane (it can appear as if your projects are somehow contained by the Library entry - not an unreasonable assumption) it actually doesn't. The Library entry doesn't hold images or projects, it simply allows you to select different filters for automatically culling images from your entire library, not just from specific projects. If you want to look at all of the 5-star images in your library, just click on the 5-star entry and allof the images in your library that have 5-stars will be displayed. Opening or closing the Library entry does not show or reveal Projects, though.

2. An album in one project can contain images from another project. While, hierarchically, an album inside of one project appears as if it's restricted to images within its parent project, you can actually drag an image from any other project into that same album. Albums are entirely project independent - they can exist inside or outside a project, and can contain an image from any other project. As always, when you add an image from a different project, only a reference to that image is stored inside the album.

Finally, remember that Albums - and Smart Albums - can sit inside or outside of a project, and that you can constrain the scope of a Smart Album by placing it in a folder along with the projects that you want it to mine images from.