[Geopriv] Proposal for uncertainty

[Martin Thomson <[e-mail]>]

I spoke about the one remaining issue with -uncertainty yesterday with
Ray.  That conversation, along with Roger's comments regarding
automated location determination helped me realize what I think the
source of the disconnect here is.

Based on this, I've tentatively concluded that the difference between
civic and geodetic location is not what is at the core of the issue,
though it's probably true that the issue only manifests with civic
location information.  Primarily because of our better intuition
regarding civic addresses.

The core of the concern is that confidence - as a statistical measure
- doesn't really make any sort of sense for location information that
is a bald assertion, as opposed to locations that are generated by
some measurement process (and here I give a nod to Carl for pointing
out reverse geocoding as an example of a measurement process that ends
with civic location).  For example, the assertion "I am at home" is
verifiable and basically either correct or not, usually the former.

It's only when taken in a larger context that terms like "confidence"
even apply.  In particular, that means automated location
determination.

I've taken a stab at clarifying this in the draft.

I've also permitted 100% confidence in the schema.  At the same time,
I've retained the text describing this as impossible, but that text is
all in the context of the statistical work, so I hope that the
introductory material makes that clear enough.

The changes are here:
https://github.com/martinthomson/drafts/commit/c2207408af95de74d1f4bb7d790965d69d4b3045
A readable copy is here:
http://martinthomson.github.io/drafts/draft-ietf-geopriv-uncertainty.html

Happy as always to take suggestions.  I'd like to think that this
helps address Marc's concern without needing to cut Section 3.3
entirely.