[Tagging] Another multipolygon question

Adam Franco adamfranco at gmail.com
Mon Oct 22 16:35:05 UTC 2018

Hi Dave, all,

Based on this discussion I just recorded this short tutorial
<https://youtu.be/x7SPb0JtheA> of how I use JOSM and its Relation Toolbox
plugin to to add adjoining land-cover areas as multipolygons with shared
boundary ways to reduce duplication and overlapping ways.

The area I'm editing, is replete with examples of this type of mapping:

The tools used are:
* JOSM editor - https://josm.openstreetmap.de/
* "Relation Toolbox" JOSM plugin -

Documentation on MultiPolygons in the OSM wiki:
* https://wiki.openstreetmap.org/wiki/Multipolygon_Examples
* https://wiki.openstreetmap.org/wiki/Relation:multipolygon

For some reason I've gotten hooked on mapping landcover in my area and
spend a lot of time adding multipolygons to do so. I find them vastly
easier to manage, update, and fix than simple closed ways with overlapping
edges (how I started). As I show in the video, adding detail usually just
means splitting exiting ways and adding/subtracting using the Relation

Hope this helps someone -- let me know if there are particular cases or
questions and I'd be happy to record another video covering other


On Mon, Oct 22, 2018 at 8:47 AM Paul Allen <pla16021 at gmail.com> wrote:

> On Mon, Oct 22, 2018 at 5:27 AM Dave Swarthout <daveswarthout at gmail.com>
> wrote:
>> Great. But what are you actually doing when you "sort the members" of a
>> relation? And after sorting, how does one "ensure the members are
>> connected"?
> Sorting something like a bus route ensures that the various ways that
> constitute it are connected
> nose-to-tail.  This is what "ensures the members are connected" and
> ensures they are connected
> in a sensible fashion.  Sorta.  It may not do a good job if the route
> traverses the same way in the
> same direction more than once.
> I've noted with dismay the lack of debugging support for relations. For
>> example, I will get an error message when trying to upload an edited
>> relation but when I ask JOSM to Zoom to the error, the display zooms out
>> enough to include the entire relation with no clue as the where the actual
>> problem is. Same thing when you ask to "jump to the next gap". Good luck on
>> that also. Maybe it's just me?
> Nope, it's not just you.  I too have problems getting my head around
> JOSM.  I use it when I have to,
> to merge or split areas (such as when I find out that a large forest that
> somebody else mapped
> has two named chunks).  It's probable I find it hard to use because I
> don't use it enough, which means
> I don't use it much, which means...  But I also have to admit that I find
> Java programs in general are
> not a good fit with how my mind expects things to work and they all give
> me a steeper learning curve
> than non-Java programs.  Which means I try not to use them much, which
> means...
> --
> Paul
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