Nice post on Nico’s WP blog on the reason why people will geo-annotate physical place. The author, Jason Tester, describe a possible categorization for these annotations. First of all he divide these contributions in two big groups:
– I was here (the author wants the receiver to know s/he was there)
– You are here (the author has some information useful for the receiver for the receiver in that location).

The former is for the author more emotionally driven, although they are still meant for other people, and for the receiver the value will be to participate in someone else’s unrecorded history of a place.

The latter can offer more utility to the viewer and the emitter, and can span into several categories:
– announcements
– events
– tips/assistance/warnings
– lost&found
– temporary notes
– gaming
– none of the above

In a previous post I sketched one categorization we did during a spatial brainstorming:

recommending system (good/bad), help, threaded discussion, wiki-like (to reach a consensus), reminder system, spam/virus/breakdown, I’m late, anchors (like rave party system), synchronous/asychronous use, query (anybody wants to paly tennis here?), crowd scenario…

Many different criteria may apply to define a proper categorization. The question is then: Can we find a criteria that is based on the collaborative activity running between the emitter and the receiver rather than on the content of the message? Is this kind of criteria going to be more universal?