# [Tagging] Another multipolygon question

Dave Swarthout daveswarthout at gmail.com
Fri Oct 26 02:39:12 UTC 2018

```Thanks again, Adam.

That was also helpful. It brings up a question about sorting. After
sorting, are the elements arranged according to their coordinates, that is
to say, spatially? Or nearest node at each end of a member way is checked
to see which other node ways are closest? Or what?

On Wed, Oct 24, 2018 at 11:02 PM Adam Franco <adamfranco at gmail.com> wrote:

> 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:
> https://youtu.be/87nRQHuatOE
>
> Cheers!
>
> On Wed, Oct 24, 2018 at 9:35 AM Dave Swarthout <daveswarthout at gmail.com>
> wrote:
>
>> 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."??
>>
>>
>> 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
>> Chiang Mai, Thailand
>> Travel Blog at http://dswarthout.blogspot.com
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>

--
Dave Swarthout