[Geojson] : Metadata ?

[Christopher Schmidt]

On Tue, Oct 02, 2007 at 08:35:44PM +0200, Guillaume Sueur wrote:
> Aren't you afraid that a data from which you don't know the origin, 
> definition, reference scale, precision and so on is a kind of ... useless ?

Nope.

To take another example: 

I have a shapefile from MassGIS. It comes with attribute data. However,
other than the datatypes, I don't know much about it: what is it of?
what do the attributes mean? etc.

However, there is a wonderful webpage where I can look all this
information up. It tells me who maintains the data, what the attributes
mean, what the projection is, etc.

Does this mean that the shapefile is useless? Not to me -- it just means
that I need additional metadata before I put it to its full use.

> I work on several governement projects in France and the mainstream is 
> to reference and validate the data accessible on the web. 

A sane policy.

> If GeoJSON 
> aims to replace WxS protocols I think there's something to consider 
> here. No ?

GeoJSON is a data exchange format -- *not* a protocol. In the same way
that HTML is a data format -- the protocol it rides on top of is HTTP.
HTTP offers additional information about the data -- content-type,
encoding, language, etc. A protocol for doing exchange of GeoJSON data
would need to mimic these types of behaviors as they apply to geo. 

Depending on the protocol, this might be a reference to the schema in
the HTTP headers. It might be a "schema_url" property on the
FeatureCollection. It might be any number of things -- all above the
level of the Feature Exchange mechanism that is GeoJSON. 

There are a couple people out there with thoughts about schemas for JSON
data. I'm not among them. I've never used an XML schema -- I've even
tried a couple times, and failed. I don't see GeoJSON's lack of schema
as any more limiting than the lack of a schema in shapefiles: the
benefit is that JSON data is extremely extensible, so if you want to
exchange that data in the format, or alongside the format, or in a
completely seperate format, you have all those options available to you.

It's important to realize that GeoJSON is not a format. It's a geometry,
and feature exchange language. Describing what a feature is is a great
candidate for another level of specification -- one I have no need for
or interest in, unfortunately for those who like my heavy-handed
dealings with specification creation :)

Regards,
-- 
Christopher Schmidt
MetaCarta