[Tagging] Another multipolygon question

Kevin Kenny kevin.b.kenny at gmail.com
Sun Oct 21 22:52:33 UTC 2018

On Sun, Oct 21, 2018 at 7:34 AM bkil <bkil.hu+Aq at gmail.com> wrote:

> It seems many would find a short video tutorial depicting these steps very
> handy. Would you mind sharing on Bitchute or on some other video hosting
> site?

On Sun, Oct 21, 2018 at 9:00 AM Dave Swarthout <daveswarthout at gmail.com>

> I was wishing that someone would write a short tutorial about relations,
> the various concepts about tagging them, and problem solving when something
> goes wrong with one. I have been unable to understand with any degree of
> certainty how and why we create them, which is the reason I started this
> thread and contributed to the other one about tagging groups of lakes. The
> Wiki is helpful but leaves out a lot of details. A tutorial, video or
> otherwise, would be extremely helpful.

On Sun, Oct 21, 2018 at 1:24 PM Mateusz Konieczny <matkoniecz at tutanota.com>

> Maybe improving wiki would be a good idea as the first [step].

I find that video tutorials don't often fit my learning style, so I don't
often use them and have never made one. Moreover, I'm an old man and
somewhat set in my ways. Nevertheless, they seem to be demanded, and if
nobody else steps forward, perhaps it will be possible to teach this old
dog that new trick.  I'd be willing to take a whack at a written tutorial,
but can't promise any particular time frame. Just at the moment, I'm
chronically busy.

The right place might be the Wiki, but I've two reservations. First, I've
simply burnt my fingers too many times when touching a Wikipedia page.
Perhaps this community is a trifle less fiery? Second, what I've seen on
OSM's Wiki (as well as Wikipedia and others) is that editors jump in to add
details that make the presentation more "correct," but less approachable to
a newcomer. For an introductory tutorial, this drift is disastrous, because
introductory material frequently is in the form of a "lie to children"
https://en.wikipedia.org/wiki/Lie-to-children that is not techinically
accurate, but provides enough of a mental model to do simple things and
prepares the mind to accept a more complete explanation later.

One thing that I will surely not be able to accomplish is to ferret out all
the obsolete and misleading information about relations that there is on
the Wiki. The community has had a complex history of groping toward a
theory of relations as it stands today, with several false paths along the
way. For example, I'm pretty sure that there are still Wiki pages out there
advising to place the tags that belong to a multipolygon on the (presumed
unique) outer ring. Moreover, there is bound to be similar groping in the
future as we grapple with representing ever more complex things, e.g.,
"traffic must stop at this intersection, except for right-turning traffic
in the rightmost lane, which need only give way to conflicting traffic," or
"this parking field is exclusively for the use of these three stores, all
of which are some distance down the street, not contiguous with it."

Nevertheless, there are particular relations that are surrounded by
considerably less remaining controversy and supported by extensive usage.
Among these are multipolygons, administrative boundaries (really a special
case of multipolygons, but we got there by a different path), waterways
(again, a special case of multipolygons, and this time, multipolygons
provide an acceptable alternative), and routes (bus, road, hiking, cycling,
etc.)  A tutorial or series of tutorials could certainly cover these
relations and leave the fine details, about which we quite rightly love to
argue, to a more advanced student.

I'm certainly unable to create such a help page or tutorial but someone
> with more experience should. I use relations often but when one develops an
> error, I'm usually hard pressed to fix it. As OSM becomes ever more
> sophisticated the learning curve gets steeper and mappers, especially
> beginners, will make tons of errors when using relations and won't have any
> idea how to go about fixing them.

 If I were to take on this task (again, no guarantees about the time
frame), I could certainly address this issue with JOSM (and possibly
Meerkartor). I surely do not know Potlatch2, iD, or any other tool well
enough to manage anything but the simplest of relations in it, nor do I see
obvious things in the UI that would do what I need. It may well be
limitations of the tools, rather than limitations of knowledge and
training, that make people assert that relations are unmaintainable or that
drawing complex boundaries twice is easier than creating multipolygons with
shared ways. That last statement, however, may be nothing but a base libel
based on ignorance. In that case, I'm more than willing to be enlighened.
It would occasionally be handy to be able to make a quick change to a
multipolygon when I'm away from a machine that has my preferred tools and
simply working in a browser.
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