An iPhoto library can hold up to 250,000 photos. That's a lot of images; in fact, it's so many that you may wonder why you'd ever need to break your existing iPhoto library into multiple ones. The answer is, you probably don't have to break single library up, but you may want to do it anyway, to better organize your images or to improve iPhoto's performance. By using multiple libraries, you can reduce the total number of photos iPhoto has to load, thus ensuring snappier performance.
You can also save time, because the time it takes to scroll though a large library of images can be considerable. And while Albums and Smart Albums can help with organization, you may find that it takes even longer to find an image when you have to try to figure out which of your many albums contains the image.
Multiple libraries can also help you focus on the topic at hand, instead of being distracted by unrelated images.
Multiple iPhoto Libraries - What You Need
To create multiple iPhoto libraries, you're going to need the following:
Plenty of storage space. You might think that the amount of drive space you're currently using for your iPhoto images is sufficient, but during the process of creating multiple libraries, you'll be duplicating some iPhoto master images. This can require a great deal of storage space, depending on the format the masters are stored in (JPEG, TIFF, or RAW).
After you finish creating multiple libraries, and you're satisfied with the results, you can delete the duplicates, but until then, you'll need the extra storage space.
An organizational plan. Before you begin, you need to have a good idea of how you will organize your images into multiple libraries. Since iPhoto can only work with a single library at a time, you need to decide in advance how you're going to divide up your images. Each library should have a specific theme that doesn't overlap other libraries. Some good examples are work and home, or landscapes, vacations, and pets.
Plenty of free time. While creating libraries and adding photos is a relatively speedy process, it can take a fair amount of time to come up with a good organizational plan. It's not uncommon to go through multiple iterations of a library structure before hitting on the one that feels right. Remember: Until you're sure you're satisfied with the results, don't delete the duplicate masters stored in your original iPhoto library.
With the above as background, let's get started with creating and populating multiple iPhoto libraries.