[OSM-dev] Source tag on each node
I've just realised that rather many nodes have their own source tag, even if they are just part of a way with identical tag. So I guess a rather large part of the data consists of these source tags. While this isn't a problem for files (thanks to compression) it enlarges the database quite a bit. Are these tags really necessary or could they be remove as long as the way has a source tag? Could anybody provide an estimate how much space reduction could be gained? Could anybody create a report on how many nodes have identical tags as their way? Wyo ___ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/dev
Re: [OSM-dev] Source tag on each node
At 2010-12-19 00:59, Wyo wrote: I've just realised that rather many nodes have their own source tag, even if they are just part of a way with identical tag. So I guess a rather large part of the data consists of these source tags. While this isn't a problem for files (thanks to compression) it enlarges the database quite a bit. Are these tags really necessary or could they be remove as long as the way has a source tag? Could anybody provide an estimate how much space reduction could be gained? Could anybody create a report on how many nodes have identical tags as their way? Do you have an example? I tag intersections of ways as I survey them with source=*, source_ref=* among other things, like signalling, turn restrictions, etc. Sometimes, the source value is the same as that of the way, but that is only coincidental - it's not a duplication. -- Alan Mintz alan_mintz+...@earthlink.net ___ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/dev
Re: [OSM-dev] Source tag on each node
On Sun, Dec 19, 2010 at 09:59:36AM +0100, Wyo wrote: I've just realised that rather many nodes have their own source tag, even if they are just part of a way with identical tag. So I guess a rather large part of the data consists of these source tags. While this isn't a problem for files (thanks to compression) it enlarges the database quite a bit. Are these tags really necessary or could they be remove as long as the way has a source tag? Could anybody provide an estimate how much space reduction could be gained? Could anybody create a report on how many nodes have identical tags as their way? As you say tagging source on nodes is generally not necessary if the only thing they do is support a way that has a source tag. http://taginfo.openstreetmap.de/keys/source#values and http://taginfo.openstreetmap.de/sources/db tell you some numbers: There are 34 Mio source tags on nodes. Note that the percentage for the node is given relative to the number of nodes that have at least a single tag. So about 50% of the nodes with at least one tag have a source tag. Only about 8% of nodes have any tag. So that means only about 4% of all nodes have a source tag. The 34 Mio source tags are about 6% of all tags (527 Mio) in the database. So in the very best case we would save 6% of tag storage space, but there is much more stuff in the database and of course not all source tags could be removed. So my estimate is that we'd actually save less than 1%. Thats not really worth any effort. And removing tags actually grows the database because there is now a new version to keep track of. So its even less worth. :-) Jochen -- Jochen Topf joc...@remote.org http://www.remote.org/jochen/ +49-721-388298 ___ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/dev
Re: [OSM-dev] Source tag on each node
Alan Mintz wrote: At 2010-12-19 00:59, Wyo wrote: I've just realised that rather many nodes have their own source tag, even if they are just part of a way with identical tag. So I guess a rather large part of the data consists of these source tags. While this isn't a problem for files (thanks to compression) it enlarges the database quite a bit. Are these tags really necessary or could they be remove as long as the way has a source tag? Could anybody provide an estimate how much space reduction could be gained? Could anybody create a report on how many nodes have identical tags as their way? Do you have an example? See http://www.openstreetmap.org/edit?lat=47.17473lon=4.71559zoom=17 where the nodes of the canal way have identical values. I tag intersections of ways as I survey them with source=*, source_ref=* among other things, like signalling, turn restrictions, etc. Sometimes, the source value is the same as that of the way, but that is only coincidental - it's not a duplication. Sorry I don't understand that. Since nodes obviously inherit (by understanding) anything from their ways, the values either must be different to show different info or they don't carry any info. Wyo ___ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/dev
Re: [OSM-dev] Source tag on each node
On Sun, Dec 19, 2010 at 11:21 AM, Wyo otto.w...@orpatec.ch wrote: Do you have an example? See http://www.openstreetmap.org/edit?lat=47.17473lon=4.71559zoom=17where the nodes of the canal way have identical values. In France and for nodes sourced cadastre, it's probably coming from an earlier version of the JOSM plugin cadastre-fr which did attached the source tag onto all objects. This is not any more the case since a while but someone should clean-up the old nodes if they don't have another tag and are not part of a way. Pieren ___ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/dev
Re: [OSM-dev] Source tag on each node
At 2010-12-19 02:21, Wyo wrote:
Alan Mintz wrote:
At 2010-12-19 00:59, Wyo wrote:
I've just realised that rather many nodes have their own source tag, even
if they are just part of a way with identical tag. So I guess a rather
large part of the data consists of these source tags. While this isn't a
problem for files (thanks to compression) it enlarges the database quite
a bit.
Are these tags really necessary or could they be remove as long as the way
has a source tag? Could anybody provide an estimate how much space
reduction could be gained? Could anybody create a report on how many nodes
have identical tags as their way?
Do you have an example?
See http://www.openstreetmap.org/edit?lat=47.17473lon=4.71559zoom=17
where the nodes of the canal way have identical values.
Oddly, only some of them. I agree that these seem duplicative (and I don't
see the need for such a long value, where cadastre_2009 would convey the
same info).
I tag intersections of ways as I survey them with source=*, source_ref=*
among other things, like signalling, turn restrictions, etc. Sometimes, the
source value is the same as that of the way, but that is only coincidental
- it's not a duplication.
Sorry I don't understand that. Since nodes obviously inherit (by
understanding) anything from their ways, the values either must be
different to show different info or they don't carry any info.
I don't agree that they necessarily inherit from their ways. A node along a
street is not named, not functionally classified (i.e. highway=primary), etc.
The situation I was referring to was this:
I tag a street: { source=survey;image;usgs_imagery +
source_ref=AM909_DSCN1234 + name=Foo Street } after tracing it from
satellite imagery, then surveying it and taking a pic of the street sign
(id'd by the source_ref) somewhere along the way.
Somewhere along this same street may be a node tagged {
highway=traffic_signals + source=survey;image;yahoo_imagery +
source_ref=AM909_DSCN5678 } indicating that I surveyed it, took a pic,
and positioned the intersection according to (different) satellite imagery.
While the two may share the survey;image sources, that is only
coincidental, not duplicative. There may be other nodes along the way that
I have not surveyed or taken pics of, which do not have tags.
--
Alan Mintz alan_mintz+...@earthlink.net
___
dev mailing list
dev@openstreetmap.org
http://lists.openstreetmap.org/listinfo/dev
Re: [OSM-dev] Source tag on each node
On Sun, Dec 19, 2010 at 11:20 PM, Alan Mintz alan_mintz+...@earthlink.net wrote: At 2010-12-19 02:21, Wyo wrote: See http://www.openstreetmap.org/edit?lat=47.17473lon=4.71559zoom=17 where the nodes of the canal way have identical values. Oddly, only some of them. Based on the node IDs, I'd venture a guess that this is because some of the nodes (the ones without a source tag) were added later (and quite possibly from a different source). It's wasteful, but then, without changes to the API, it's hard to see how to provide the same information with less waste: Not all nodes on a way are necessarily from the same source. ___ dev mailing list dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/dev
