Date (tag)
From SnapMap
date=<date> is the main method of specifying the date that the photograph was taken, or, in general, the date that an image depicts. Date is separate from time (tag), but both may be specified together using datetime (tag).
The main form is:
- date=YYYY-MM-DD
But, if only the year and month are know, it can be shortened to:
- date=YYYY-MM
And, if only the year is know, to:
- date=YYYY
Decades and centuries are denoted respectively:
- date=YYY0s
- date=18th century
Date ranges are denoted using '..' (not '...'), thus:
- date=YYYY-MM-DD..YYYY-MM-DD
- date=YYYY-MM..YYYY-MM
- date=YYYY..YYYY
Also allowable are:
- early YYYY
- mid YYYY
- late YYYY
- early YYY0s
- mid YYY0s
- late YYY0s
- early YYth century
- mid YYth century
- late YYth century
- spring YYYY
- summer YYYY
- autumn YYYY
- winter YYYY — not recommended, since the intended year is ambiguous
- cYYYY (i.e. circa YYYY)
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Multiple possible dates
It may be that it is known only that a photo was taken on one of several possible dates. For example, if we know the book in which a photo of Remembrance Sunday, in which the Cenotaph in London appears, was published in 1926, and we also know a) the Cenotaph was built in time for the November 1920 commemoration, and b) Remembrance Sunday takes place on the Sunday nearest to November 11, we can state that the date was one of 7 possibilities:
webpage=http://www.flickr.com/photos/wonderfullondon/433411470/ date=1920-11-14 date=1921-11-13 date=1922-11-12 date=1923-11-11 date=1924-11-09 date=1925-11-08 date=1926-11-14
Currently just one of these makes its way into the SnapMap image cache. Improved options would be to choose the mid-point, the mean, or the median value; or possibly even to handle multiple cached dates.
User agents and approximate dates
User agents are encouraged to handle approximate dates, if they choose not to present the range itself. Using a date exactly in the middle of the range is one option. A randomized date in the range is another possibility, which would nicely avoid stacking items of various dates onto a particular date, but have the disadvantage of given an apparent precision to vague data. User agents might wish to make sure photos with vague dates do not appear in the UI much more often than those with precise dates.
Creation date
For imaginative renderings of scenes, whether the depicted date is in the past or the future, we use creation_date (tag) for the date the image was made, and still use date for the date the image depicts. Here's an example of date tags for an image created in 1961 of Roman London:
date=1961 creation_date=150
By contrast, an architectural perspective of a building not yet built would have creation_date earlier than date.
