[Talk-ca] Multipolygon problems

john whelan jwhelan0112 at gmail.com
Fri Jun 30 19:11:15 UTC 2017

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

I remember the days when it was trudge out in the rain with the Garmin then
upload the GPS traces only to find a straight road was no longer straight
because of the wet leaves in the trees above.

Cheerio John

On 30 June 2017 at 15:03, James <james2432 at gmail.com> wrote:

> 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
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