[Talk-us] Large-scale Data Imports and Tags on Nodes

Christopher Schmidt crschmidt at metacarta.com
Thu Jan 8 02:10:56 GMT 2009


On Wed, Jan 07, 2009 at 05:38:34PM -0800, Sam Vekemans wrote:
> I cc'd to talk-ca list, as it's also relevant.
> 
> I do see our point Ian, as when i look through, south of the border, i have
> no actual need to be seeing all these extra tags.
> Yes, they are relevant, but only for the person(s) who are using those tags
> for the update program.
> 
> So really, all that is needed is the tag that says it's source, and the NID
> tag. ..  Since the python script only really needs to know weather or not
> that point/way actually exists. .. from there, it compares to the OSM tags.
> the tag "nrn:datasetName=Ontario" is that Really needed?

I have a different feeling on this. First of all, if errors are found,
knowing where the source data is from -- to the point that you can find
the bytes neccesary to look at what the source was -- can be useful.

Second of all, I think that, within a namespace, extra tags aren't a bad
thing. One of the targets I have for the MassGIS OpenSpace dataset is to
make it possible to take that data back *out* again -- and not just the
OSM improvements to it, but to essentially make it possible to get the
data file that the source came from back out -- with improvements.

To that end, the MassGIS OpenSpace import included *all* o the non-null
tags on the source, so that the data could be recreated.

The cases this doesn't apply to, in my opinion, are the cases when the
elements you are creating -- nodes, usually -- aren't actually included
as seperate, tagged entities in the source. Shapefiles will amost always
have this as the case; they are non-topological, so the *nodes* are just
strings in the shapefile. Turning them into nodes is an OSM task, not a
shapefile one.

> It's only at the GeoBase side that the tag would be useful. ... searching
> for all the roads in the Ontario dataset of the National Road Network. ...
> so the purpose of having this would be;
> 1 - if we wanted to remove all the data (from a planet.osm dump)
> 2 - if we wanted to replace this dataset with a new one, we would have a tag
> to go by.
> 
> the tag "is_in=Ontario" would that not say the same thing?

Probably not, but I don't know about the GeoBased data enough to be
sure. At the very least, Mass lakes data extends outside massachusetts
-- and even if you kept the is_in tag, someone might delete it down the
road.

Regards,
-- 
Christopher Schmidt
MetaCarta




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