Twitter posts like this one:
have a place- name and corresponding coordinates (indicated by the prefix “l:”). This has allowed them to be plotted on a map.
It should be possible for the poster to send, say:
We’re still deep in the Sundarbans, near Tambulbunia, meeting experts on dolphins and tigers. #hcard: fn+locality:Tambulbunia: country-name:Bangladesh: geo:22.27722,89.71905
using colons as delimiters and have Twitter render that comment marked up as an hCard.
In the short term, this could be achieved by a third-party site, like #hashtags .
UPDATE: being more mindful of the 140 character limit than I have in the above example, perhaps class names might be abbreviated (“loc” for “locality”, “ctry” for “country-name”, and so on).