Tuesday, December 20, 2011

Pleiades, Flickr, and the Ancient World Image Bank

Many of you are already aware that Pleiades, Flickr, and the Ancient World Image Bank have joined forces to link together online, open-access imagery and ancient geographical information. This blog post is intended to answer some lingering questions that users and potential contributors have been asking about the process.

Other Blog Posts
How to Construct a Pleiades Machine Tag

In Flickr, you add the machine tag the same way you add regular tags when editing an individual image or a set or group in the organizer. The machine tag should use the following syntax:
where "TERM" is one of the recognized terms (originally from the Concordia Thesaurus, aka the Graph of Ancient World Data, or GAWD, terms) listed below and "#####" is the numeric identifier of the Pleiades place you wish to associate with the photo.

You can get the identifier by visiting then searching for and finding the place. Copy the numeric portion of the URL of the place page and paste it into your tag.

So, for example, if I wanted to tag a photo that "depicts" ancient Athens (or a portion thereof), I'd visit Pleiades and search for Athens. I'd find this place page: So, I'd grab 579885 and construct the following machine tag for use in Flickr:
Recognized Terms in Pleiades Machine Tags

TERMS for use in Pleiades machine tags should begin with a lowercase letter. The following TERMS are recognized in Pleiades machine tags:
the photo so tagged can be said to "depict" the referenced ancient place or a significant or exemplary portion thereof
(this term is equivalent to CIDOC CRM p62 "depicts")
the photo so tagged shows an object that was first found in modern times at the referenced ancient place
(this term is particularly useful for items now in museums or elsewhere, especially those no longer at the initial place of finding)
the photo so tagged shows an object that is believed, with reasonably high certainty, to have been originally located or produced at the referenced ancient place
(this can differ from the findspot, as when an inscription or other object was moved in antiquity)
the photo so tagged shows an object that was observed in modern times at the referenced ancient place
(the implication being that the place observed is neither the modern findspot nor the presumed original location; I suspect this term will rarely need to be used to link photos with Pleiades place resources)
the photo so tagged is related in some way to the referenced ancient place, but for some unspecified reason no more specific relationship can be asserted
(this term should not be used unless none of above terms are deemed to be appropriate)
this term is DEPRECATED; it was originally used in exploring the Pleiades machine tag idea (and is highlighted in my previous blog post). Its semantics are assumed to be equivalent to "where". If at all possible, photos carrying this tag should be updated to use one of the more specific terms above.

Please note that pleiades:places=##### (i.e., with a plural) is not a recognized machine tag. Its behavior in Flickr or Pleiades is undefined. So is the behavior of any Pleiades machine tag with a misspelling or a term not included in the list above. ("finspot" seems to be a popular typo at present).

Any photo tagged with the proper Pleiades machine tag syntax and one of the terms above will be noticed by Pleiades and picked up in the summary counts and links on individual place resource pages. In order for a photo to be considered for the Pleiades Places group on Flickr (and therefore as a "portrait image" for a Pleiades place), the photo must be tagged with a pleiades:depicts tag.

How do I Add Pleiades Machine Tags Quickly?

It would be unreasonable of us to ask a prolific photographer with an extensive, well-tagged collection already on Flickr to go through an individually add appropriate machine tags by hand. Fortunately, Flickr provides a mechanism for easy batch editing of tags.
  1. Suppose that you have tagged a large number of your photos with the name of the ancient site (e.g., Halicarnassus)
  2. Visit the following link:; it will give you an alphabetical list of all your tags.
  3. Find the name of the site and click on the corresponding link. You'll see all the photos thus tagged in your photostream.
  4. Find and click on the "Change this tag" link (Really. Skip "Edit these in a batch" link for now).
  5. Insert the cursor after your existing tag string, type a space, then type or paste in the desired Pleiades machine tag (read the fine print on that page for an extended explanation of what's going on).
  6. Click the "save" button. Flickr will go off and add the new tag to all those images at once.
  7. If you'd rather be more selective about which photos you want to add a tag to, you can choose the "Edit these in a batch" link I told you to skip above, then paste the Pleiades machine tag into the tag lists associated with only those images you wish to update.
Why Can't We Just Use Geotagging That's Already in the Photos?

Some photographers have geotagged their photos, either using a GPS-enabled digital camera or some method of post-processing. I was recently asked on twitter why we're putting people to all the trouble above when we could just use the geotagging? There are several reasons:
  • Not everybody's photos are machine-tagged.
  • Many ancient sites are coincident with urban areas (or areas of natural beauty or places where someone took a picture of their dog) and so mere proximity to an ancient site can't be interpreted as indicating a given photo is relevant to a nearby Pleiades place.
  • Horizontal precision and accuracy can vary widely in geotagged photos as a function of the geotagging method used and the interests and skill of the person doing the geotagging. As a result, a photo might be geotagged at a location closer to another, unrelated pleiades place.
  • The horizontal precision and accuracy of Pleiades coordinates also varies widely given the varying sources from which it derives and the subsequent coordinate extraction methods. This makes the process of proximity correlation even more fraught.
This is not to say that we're not interested in exploring uses for geotagged photos in Flickr (or supporting a geotag-your-photo-using-Pleiades-coordinates tool), but I hope this discussion helps explain why we like the machine-tag approach for indicating relevance.

Please let me know, via comments here, if you have additional questions or suggestions.