[Talk-ca] Multipolygon problems

James james2432 at gmail.com
Fri Jun 30 19:03:59 UTC 2017

Especially when the only imagery available is Landsat....

On Jun 30, 2017 2:18 PM, "Frank Steggink" <steggink at steggink.org> wrote:

> 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.
> Regards,
> Frank
> [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
>>> _______________________________________________
>>> Talk-ca mailing list
>>> Talk-ca at openstreetmap.org
>>> https://lists.openstreetmap.org/listinfo/talk-ca
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