[Talk-ca] Multipolygon problems

Stewart Russell scruss at gmail.com
Fri Jun 30 14:40:48 UTC 2017

Hi Jochen,

I was waiting for user canvec_imports to say something, but there's been no
activity from the account for more than two years.

The import was started a long time ago, before there were import guidelines
and very likely before the licence change too. It was done with the best
available data at the time, and done with good intent. It was a major coup
to get government data at the time.

Since we have the most of these offending polygons in Canada, and since
we're the second largest country in the world, a more bombastic version of
me might be tempted to say, "No, *you're* doing it wrong ...". But that's
not particularly Canadian, and even less constructive. We simply don't have
the community available to fix this.

One thing that we must do is ensure that the sources of Canvec import data
are either fixed or removed from the web. The infrastructure and
documentation for continuing this import and thus propagating these alleged
errors is still out there. Unless it is removed, we could potentially have
a mapper restart the import again.


On Jun 30, 2017 3:54 AM, "Jochen Topf" <jochen at remote.org> wrote:


A week ago I wrote this email and nobody answered it yet. Does that
mean that nobody feels responsible for the import that created this data
and nobody here cares for this data?

I see three ways forward:
* We do nothing. The broken data stays in OSM. Not a good solution,
  because every user of the data has to work around this or handle the
* The Canadian community steps up and fixes the data, automatically or
* We ask the Data Working Group to remove the broken import.


On Thu, Jun 22, 2017 at 11:38:15AM +0200, Jochen Topf wrote:
> Date: Thu, 22 Jun 2017 11:38:15 +0200
> From: Jochen Topf <jochen at remote.org>
> To: talk-ca at openstreetmap.org
> Subject: [Talk-ca] Multipolygon problems
> Hi!
> In the last days the OpenStreetMap Carto Style 4.0 is being deployed on
> the OSMF tile servers. This new version of the style doesn't take
> old-style multipolygons (where the tags are on the outer ways instead of
> on the relation) into account any more. In a huge effort in the last
> months we have converted all old-style multipolygons to the modern
> tagging, so this is a good step!
> Unfortunately, as a side-effect of this change, many multipolygon
> relations now appear wrong on the map. This is the case for multipolygon
> relations that have the same tags on the relation as well as on (some of
> the) outer or inner ways. This is *wrong* tagging, and needs to be
> fixed. (Note that this always was wrong tagging, even before we
> deprecated old-style multipolygons, but the way the software worked with
> old-style multipolygons, this problem was not visible on the map. But
> now it is.)
> Here is an example: http://www.openstreetmap.org/relation/1330741 . As
> you can see (unless somebody fixes this :-) the clearing in the forest
> that should just have grass, also has tree symbols on it. In many other
> cases it is not this obvious, there are just islands in a river missing
> or so.
> There are about 50,000 cases like this worldwide, forests, waterways,
> all sorts of areas. But the worst problem is in Canada. There are about
> 15,000 affected relations, most from the CanVec imports.
> First, we have to make sure that there are no further imports of broken
> data. I hope the people who have done those imports (and might still
> continue) are here on this mailing list. If not please make them aware
> of this issue and/or put me in touch with them. Second, somebody needs
> to clean up the broken data, either automatically or manually. 99% of
> the data has not been changed since the import, so it might be feasible
> to do an automatic cleanup, but somebody has to do this. Otherwise we'll
> have to do a manual cleanup, through tools such as Maproulette and the
> OSM Inspector. I am currently in the process of creating Maproulette
> challenges for other areas of the planet, but will not do this for
> Canada at this time. Lets discuss this here first.
> I can provide OSM data extracts, statistics, etc. if somebody wants to
> look at the data.
> All of this is part of a larger effort to fix areas in OSM. See
> http://area.jochentopf.com/ for more information. There is also a thread
> on the talk mailinglist at
> https://lists.openstreetmap.org/pipermail/talk/2017-June/078203.html
> and this issue
> https://github.com/osmlab/fixing-polygons-in-osm/issues/36 .
> News of the effort are posted regularly to
> https://github.com/osmlab/fixing-polygons-in-osm/issues/15 .
> Jochen
> --
> Jochen Topf  jochen at remote.org  https://www.jochentopf.com/
> _______________________________________________
> Talk-ca mailing list
> Talk-ca at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/talk-ca

Jochen Topf  jochen at remote.org  https://www.jochentopf.com/

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