Yep, there are many reasons why geographic coordinates should be reified, largely because some people need more information than others.
Today all the people who got into geography in the last few years use WGS84 as a datum so it's fashionable to not specify any datum. That goes back to the bad old days when visual surveying was the only game in town so you could specify locations on an island relative to each other quite accurately but need to get a fix against the stars to know where the island as a whole was.
Even neogeography projects, however, sometimes need to specify a datum. A while back I was collecting a data set on the Hollywood Walk of Fame and the requirements there were: (i) stars get located on the right side of the street, (ii) stars get located in the right order, and (iii) stars get located on the right block. WGS84 (a standard GPS unit) isn't quite good enough to do these three things, particularly close to the Hollywood and Vine intersection where there are some big buildings with metal in them and probably some QRM too. Satisfying those three requirements is a matter of creating your own datum which you could with some kind of DGPS or in my case merging ground observations with published data.
There also are things that have two coordinates, different levels of accuracy, altitude or not altiitude, etc and just bundling the properties together in an object future proofs you for all that.
-----Original Message----- From: Andreas Schultz
Sent: Wednesday, October 17, 2012 7:20 AM
To: wikidata-l@lists.wikimedia.org
Subject: [Wikidata-l] JSON representation
Hi all,
I have a question or rather proposal regarding the JSON representation [1].
The "Geo" example on the JSON page[1] implies that there won't be a
fixed representation for data types. Instead of the "value" key that
all the other examples use, the Geo example uses "longitude" and
"latitude". Wouldn't a representation like the following be more
appropriate?
"value": {
"latitude" : 32.233,
"longitude" : -2.233,
}
That is, if "snaktype": "value", then there has to be a "value" key
with a data type specific value object.
Something that imho would also be useful, is a way to specify the data
type - this could be optional. For the Geo example something like the
following would make sense:
"datatype": "geo"
Without such a definition, a consumer would have to derive the data
type from the keys and/or the lexical representation of the values,
which would usually be a tough task.
Cheers,
Andreas
1. https://meta.wikimedia.org/wiki/Wikidata/Development/Phase_2_JSON