Although there's little outward indication of this, iPhoto lets you create and maintain multiple iPhoto Library folders.
Reasons to create multiple iPhoto Library folders:
You might want to keep two different types of photos completely separate, such as personal snapshots and location shots for your real estate business.
You might want different iPhoto Library folders for different purposes. For instance, I have a special iPhoto Library folder that holds just a few images that I use when giving presentations.
You might want an iPhoto Library for miscellaneous photos sent to you by other people that you don't want cluttering your main collection.
To create an iPhoto Library folder:
Hold down and click iPhoto's icon in the Dock to launch it.
In the Choose Photo Library dialog, click Create Library (Figure 2.21), and in the New Photo Library dialog, enter a name and select a location for your new iPhoto Library folder (Figure 2.22).
Figure 2.21. Create a new iPhoto Library folder by holding down Option while launching iPhoto and then clicking Create Library in the Choose Photo Library dialog.
Figure 2.22. Name and save your new iPhoto Library folder however and wherever you like.
If you want a second iPhoto Library folder to contain all your photos to start with, select the original iPhoto Library folder in the Pictures folder in the Finder and choose Duplicate () from the Finder's File menu.