[Talk-ca] Multipolygon problems

James james2432 at gmail.com
Fri Jun 30 10:28:56 UTC 2017


Represents multiple thousand square kilometers of forest/objects. To
actually be able to fix it correctly you NEED to launch JOSM in 64bit mode
with min/max memory values set or else it will crap out/freeze at 2GB of
memory. Now 1. JOSM doesnt document this ANYWHERE/IS VERY VERY HARD TO FIND
for the common user. I doubt many people know about the 2gb limit(other
than power mappers) .
Personally I find it very arrogant of you to say well, it's been a week
might as well contact the DWG and revert all of Canada, cause no one
replied to my email... not everyone has the experiance needed to merge down
polygons/relations on such a large object scale and very wide spread
throughout Canada

On Jun 30, 2017 6:12 AM, "James" <james2432 at gmail.com> wrote:

The problem that canvec has is multi polygons with different attributes
were stacked on top of eachother(i.e. hole in the forest that is also a
lake? That makes 2 polygons with same shape stacked one of top of
eachother... marshland+water+hole in forest? 3 polygons etc etc. Not that I
wouldnt live it fixed, but as someone that has "fixed" canvec data before
dropping it in, It's a massive undertaking and really complexe/abstract
thing to do.

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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