[Talk-ca] Multipolygon problems

Frank Steggink steggink at steggink.org
Fri Jun 30 18:16:40 UTC 2017

Hi Jochen,

Maybe I'm not understanding it, but in the OSM inspector [1] I just see 
one case of old style multipolygon, in Manitoba. Last week, when you 
posted your original message, I just saw one case in New Brunswick. 
IIRC, it was a park, not even from the Canvec import.

In the OSM inspector other errors can be seen, but the most prevalent 
one is "Touching rings". Maybe indeed a case of suboptimal mapping, but 
nothing which seems urgent to me.

Here is an example of a forest multipolygon, imported by me 
(canvec_fsteggink). It is still version 1, but it has tags on the 
relation, not on the rings (except for the quarries): [2]
This is from Canvec v7.0. IIRC, we started at v6.0, and the last version 
I know of is v10.0. Maybe v6.0 had wrong tagging, but I'm not seeing any 
such cases in the OSM inspector.

So, I'd like to ask you to give a couple of examples where data imported 
from Canvec is clearly wrong with regard to old style multipolygon 
tagging. When we have clear examples, then it might be easier to come up 
with a plan how to fix it. But so far, I see absolutely no reason why 
Canada stands out in a negative way. Yes, we all acknowledge that Canvec 
data is suboptimal, but as others already have pointed out, mapping 
everything by hand in especially remote areas is nearly impossible.



[1] http://tools.geofabrik.de/osmi/?view=areas
[2] https://www.openstreetmap.org/relation/1481163/history

On 30-06-2017 09:52, Jochen Topf wrote:
> Hi!
> 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
>    complaints.
> * The Canadian community steps up and fixes the data, automatically or
>    manually.
> * We ask the Data Working Group to remove the broken import.
> Jochen
> 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/  +49-351-31778688
>> _______________________________________________
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