[Tagging] Another multipolygon question

Adam Franco adamfranco at gmail.com
Wed Oct 24 16:02:43 UTC 2018

My pleasure, Dave! I'm glad to have helped even a little. :-)

Here's another short (2:25) video showing how I use the Relation Editor
window to sort and find disconnected segments:


On Wed, Oct 24, 2018 at 9:35 AM Dave Swarthout <daveswarthout at gmail.com>

> They say a picture is worth a thousand words and IMO that video says
> bushels about mapping relations. I was always a bit scared when fooling
> with them because as it turns out, their reputation is worse than the
> reality. The Reltoolbox is similar to the normal relation editor as Kevin
> points out but for me it makes the task ever so much faster. You can move
> along picking up pieces of whatever multipolygon you're constructing and it
> just magically adds them. I have one place where the same way is used for a
> place=island with its name, a NWR boundary, a wood multipolygon and a sand
> multipolygon. Freakin' awesome! I've learned more in the past day while
> mapping islands in the Kodiak Archipelago than in the past 5 years of
> working with multipolygons.
> Now all we need is a video tutorial showing how to analyze one during a
> debugging episode. Talk abut sorting, perhaps, an a walk through of a
> session where there is a "gap" in some relation that you cannot locate.
> What techniques and/or tools would one use in that case? And what about
> those little squiggles that appear at the end of each member's line in the
> relation editor. I know they indicate connectivity (a closed loop?) but
> what do you do if there is a problem, a "gap."??
> Anyway, thanks again to Adam. You've advanced my understanding immensely.
> Dave
> On Tue, Oct 23, 2018 at 10:39 PM Kevin Kenny <kevin.b.kenny at gmail.com>
> wrote:
>> On Mon, Oct 22, 2018 at 12:36 PM Adam Franco <adamfranco at gmail.com>
>> wrote:
>>> 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.
>> Thanks for recording that! Now I don't have to. :)
>> Your workflow is essentially the same as mine, except that I use the
>> regular old relation editor to add and delete ways. Works well enough for
>> me, and I think it's only one or two clicks more than what you're doing. I
>> also make a lot of use of 'replace geometry' from utlilsplugin2, since a
>> lot of what I'm editing was born as imports and is being replaced with
>> updated data from the same sources. Yes, I'm very careful not to step on
>> the work of local mappers when I do it.
>> Depending on what's going on in the field, I might have called that
>> hedgerow a tree_row or a hedge and used a linear feature to map it.
>> Similarly, at breaks in tree cover for things like power lines and
>> pipelines, I might use man_made=cutline. Speeds up the process a little bit
>> more. For what it's worth, I tend to restrict the 'cutline' tag to a
>> standard (in NY) four-rod right-of-way; if the cutting is larger than that,
>> it gets a polygon.
>> Hopefully this will begin to show that for complex landcover, or
>> similarly complex admin boundaries, that multipolygons with shared ways are
>> actually quicker and easier to maintain than simple areas.  I know that
>> they're still controversial, even among experienced mappers, but for
>> something complicated like West Point
>> https://www.openstreetmap.org/relation/175474, with a whole bunch of
>> shared borders, rights-of-way cut out of it and what not, I'd be really
>> handicapped without shared ways.  I didn't get very far on the landcover
>> because I seldom map landcover other than in my own neighbourhood or when
>> fixing other people's mistakes.
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> --
> Dave Swarthout
> Homer, Alaska
> Chiang Mai, Thailand
> Travel Blog at http://dswarthout.blogspot.com
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