[Geojson] : Metadata ?

[Guillaume Sueur]

Christopher Schmidt a écrit :
> 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,

I don't agree. You must provide information to the client which receives 
geometry and features of what can be done with them. You don't compute 
thresholds the same way with different types of data. You shouldn't 
display vector data on scales much higher than their scale of 
digitalisation.
But I may have needs and interest completely out of scope !
Sorry to bother ;-)

-- 
Guillaume SUEUR
Expert SIG et OpenSource
NEOGEO
46 RUE MATABIAU
31000 TOULOUSE
06 65 58 88 82
Site web : http://www.neogeo-online.net

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