If you spend a little time training Photos' facial recognition feature, you can round up pictures of certain people (handy for slideshows and other projects). Create a smart album that includes the criteria "Face" and "is," and then pick a face tag from the third menu. Add another row that includes "Face" and "is," and pick another face tag from the third menu. Rinse and repeat until you include all the people you want in the album and then set the Match menu to any or all.
Finding certain locations
A smart album with the criteria "Photo," "is," and "tagged with GPS" gathers all your GPS-tagged images. Add another row of criteria, say, with "Text," "includes," "Manhattan," with the Match menu set to all creates an album with all the pictures you've taken (and will take) in Manhattan, New York, excluding any that contain Manhattan elsewhere in their metadata — say, in a description describing the famous cocktail you enjoyed at dinner.
If you (wisely) use keywords and you frequently use the search field to find certain ones, create a smart album that gathers them instead. That way you get all the images that currently have the keyword(s), as well as any future images you apply those keywords to. So if you keyword your flower shots with flower, create a smart album with the criteria "Keyword," "includes," and "flower." To find your macro flower shots, add another row with the criteria "Lens," "includes," and "Lensbaby Muse" (or whatever macro lens you use), and then set the Match menu to all.
Another scenario is to use keywords to rate images and then have smart albums collect your highest rated shots. For example, if you upgraded to Photos from iPhoto where you used star ratings, Photos converts those ratings into keywords: 1 star, 2 star, 3 star, 4 star, and 5 star. If you use the Keyword Manager (Command-K) to give those keywords a keyboard shortcut (say, 1, 2, 3, 4 and 5), you can keep using the same rating system in Photos that you did iPhoto. To find all your starred items, create a smart album for each rating. For example, the criteria "Keyword," "is," and "5 Star" collects all the images in your library with the 5 Star keyword.
Finding your highest rated pictures in other albums
Once you start using keywords to rate images, you can find your highest rated images in certain albums — say, the graduation album you just made. Create a smart album that includes the criteria "Keyword," "is," and "5 star." Add another row with the criteria "Album" and "is," and pick the graduation album from third menu, then set the Match menu to all. You may even add another row that uses face tags to limit the album to pictures that include the graduate (say, instead of their buddies).
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