Aperture supports hierarchical keywords (tags). I use them all the time. My eBook talks all about this. Leveraging this feature speeds up workflow. I only need to add "San Diego" as a keyword, and its parents "California", "United States", and "North America" are added implicitly. However, there is a caveat.

This is best explained with an example. Here's a small excerpt of my keywords hierarchy. I just shot some photos in Austin, Texas. When tagging the photos, I only explicitly assign the "Austin" keyword. The rest of the hierarchy is implicitly applied within Aperture. Any queries in Aperture for all photos with the "Texas" keyword will include "Austin" (and "Dallas", and "Houston", and so on).

So far, this is great. Fewer keywords to assign, a faster workflow. Now the caveat. When versions or originals are exported, only the explicitly assigned keywords are exported. I tried a variety of exports:

• Export a version with metadata
• Export the original including the IPTC metadata
• Do "Metadata > Write IPTC Metadata to Original" and export the original including the IPTC data

Using exiftool to check the results:

This is less desirable if your version will be used online in Flickr, 500px, and the like for licensing. The more tags your photo has, the more likely it will be found by a potential client.

The solution? Coming soon. I'm working on an AppleScript to create a version with a "flattened" set of keywords. Once I've got it working and stable, I'll share it here.

Update: The script in available in the store now. More details here.