Multipolygonizing

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Multipolygonizing

Doug Hembry
Greetings everyone,
I've just had a short changeset discussion with mapper glebius prompted
by changeset 46612750 "Properly multipolygonize Monterey coast line". My
understanding is that the map of this stretch of coastline has been
restructured to avoid adjacent ways that share nodes. Accordingly, only
a single way ever connects any set of nodes, and the single way
participates, if necessary, in multiple relations. A result of this is
that in a high density area like downtown Monterey Bay many small areas
like building footprints or pedestrian areas are defined as distinct
multipolygons, with several ways (outers) making up the outline. An
example at:

https://www.openstreetmap.org/#map=18/36.61726/-121.90045

(look at Hovden Way near the top, or the outline of 700 Cannery Row,
further down near Bubba Gump, comprised of seven outer ways)

glebius believes that this approach (with the help of the reltoolbox
JOSM plugin) is easier and less error-prone than having multiple simple
closed ways (eg, a building footprint and an adjacent pedestrian area)
sharing a set of nodes on their adjacent boundary. . (I hope I'm
representing this accurately, glebius will correct me if I'm getting it
wrong).

In my limited experience I've never encountered this before, and at
first sight I'm not convinced, particularly when considering future
maintenance. I told glebius that I wanted to find out  what the
community thought. Is this just one more valid optional way of mapping?
To be recommended for adoption if possible? Or to be avoided? Thoughts?

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Re: Multipolygonizing

Rihards
On 2017.11.20. 00:48, Douglas Hembry wrote:

> Greetings everyone,
> I've just had a short changeset discussion with mapper glebius prompted
> by changeset 46612750 "Properly multipolygonize Monterey coast line". My
> understanding is that the map of this stretch of coastline has been
> restructured to avoid adjacent ways that share nodes. Accordingly, only
> a single way ever connects any set of nodes, and the single way
> participates, if necessary, in multiple relations. A result of this is
> that in a high density area like downtown Monterey Bay many small areas
> like building footprints or pedestrian areas are defined as distinct
> multipolygons, with several ways (outers) making up the outline. An
> example at:
>
> https://www.openstreetmap.org/#map=18/36.61726/-121.90045
>
> (look at Hovden Way near the top, or the outline of 700 Cannery Row,
> further down near Bubba Gump, comprised of seven outer ways)
>
> glebius believes that this approach (with the help of the reltoolbox
> JOSM plugin) is easier and less error-prone than having multiple simple
> closed ways (eg, a building footprint and an adjacent pedestrian area)
> sharing a set of nodes on their adjacent boundary. . (I hope I'm
> representing this accurately, glebius will correct me if I'm getting it
> wrong).
>
> In my limited experience I've never encountered this before, and at
> first sight I'm not convinced, particularly when considering future
> maintenance. I told glebius that I wanted to find out  what the
> community thought. Is this just one more valid optional way of mapping?
> To be recommended for adoption if possible? Or to be avoided? Thoughts?

not an authoritative opinion : it's terrible. mapping contiguous areas
as multipolygons results in data that is extremely hard to modify (think
splitting landuse from a building) and is more than a minefield for newbies.

personally, i either redo these as separate ways when i have the time
(original authors do not object as they have went either mad or out of
energy after working with multipolygons too much), or give up and leave
the area outdated - i don't have the skills to maintain that.
--
 Rihards

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Re: Multipolygonizing

Mike N.
In reply to this post by Doug Hembry
On 11/19/2017 5:48 PM, Douglas Hembry wrote:
> I told glebius that I wanted to find out  what the
> community thought. Is this just one more valid optional way of mapping?
> To be recommended for adoption if possible? Or to be avoided? Thoughts?

   I have this situation locally where much of the adjacent landuse was
created as multipolygon.  It definitely takes longer to modify these
areas for new construction.  That is in JOSM without that special
toolbox which I hadn't used before.

   I can't imagine what it must be like for a newcomer (with any editor).


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Re: Multipolygonizing

Frederik Ramm
In reply to this post by Doug Hembry
Hi,

On 11/19/2017 11:48 PM, Douglas Hembry wrote:
> glebius believes that this approach (with the help of the reltoolbox
> JOSM plugin) is easier and less error-prone than having multiple simple
> closed ways (eg, a building footprint and an adjacent pedestrian area)
> sharing a set of nodes on their adjacent boundary. . (I hope I'm
> representing this accurately, glebius will correct me if I'm getting it
> wrong).

He's not entirely wrong; this approach is something we have come to
expect when you have a mesh of areas, like for example county
administrative areas: One begins where the other ends, and allowing each
to have its own "way" connecting the nodes would only increase the
amount of data and complicate editing.

However, when it comes to very small areas, like adjacent buildings or
landuse areas that only share a handful of nodes, introducing a relation
seems an unnecessary complexity.

It is most often mappers with an IT background and an unwillingness, or
even inability, to accept that there can be more than one way to do it
right - they tend to follow the "everything is a multipolygon" approach.
I've occasionally had to forcibly convince them to re-think that
approach because they were essentially turning their home turf into a
creative multipolygon landscape that nobody else dared edit. This is
IMHO the foremost reason against this "multipoligonism" - you're making
things harder to edit for others.

(Another frequent hobby of multipolygon fans is combining several
disjunct areas, say three landuse=farmland areas, into one multipolygon,
because this "saves" space, since landuse=farmland then only needs to be
tagged once not three times. IMHO this is only acceptable if the three
areas have more in common than being farmland; for example if the three
areas together share a local name or so.)

Bye
Frederik

--
Frederik Ramm  ##  eMail [hidden email]  ##  N49°00'09" E008°23'33"

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Re: Multipolygonizing

stevea
In reply to this post by Doug Hembry
I very much agree with Douglas and Rihards that glebius' mapping is (around here) unusual, "terrible" and difficult to parse, even for experienced mappers who have been mapping for most of the history of OSM, like me.  Glebius is right in my backyard and I've found his coastal "restructurings" (e.g. http://www.osm.org/changeset/46756097) to be bizarre and unnecessary, often overwriting correct official (county GIS imported) data simply to not "share some nodes" or "improve the mess."  He claims that "the consensus in Russia is that advanced polygons is the way to go."  Well, not here, I assure both Glebuis and the talk-us list of that unequivocally.

Glebius uses a JOSM plugin (and it AMAZES him that this functionality has not yet been built into JOSM's base code!) called "reltoolbox."  It promulgates what he calls "advanced multipolygons" and in the below-noted changeset acknowledges that he believes these "became a world wide consensus," but of course, they have not.  Glebius has glibly assumed reltoolbox and its resulting data is widespread, when in fact it is not:  neither locally, regionally, nor continentally.  He further says the "quality of OSM data in USA is much worse than in other countries" when in fact, my small county of Santa Cruz (through a wiki-documented process of both importing local government landuse polygons and painfully though lovingly improving them over three revisions and many years) actually won a Gold Star Award at BestOfOSM.org for "nearly perfect landuse."  Well, before glebius snarled up a perfectly geometrically valid coastline and many of its landuse polygons, amenities, parks, marinas and recreation areas in Santa Cruz before I manually reverted a good number of his "fixes."

Glebius may believe he is "saving data" by "reducing overlapping nodes," but the added complexity to do this in multipolygons is distinctly confusing to many (most) OSM volunteers, especially beginners who find multipolygons confusing or intimidating.  I'm not saying glebius' practices or resulting data are wrong, but rather that when they overwrite perfectly already-correct data, his time is likely better spent on other OSM tasks.  Especially when he rudely calls correct and even award-winning data "a mess."

Please, glebius, don't do this here.  Everybody else in our community find your submissions to be confusing and difficult to maintain, this practice is ANYTHING BUT widespread (here in North America), you are overwriting valid data in a way that makes it nearly impossible to update with better data (especially when part of import updates) and whatever small cost you believe you are saving in either elegance or the amount of data in the map is very much outweighed by "simpler is better."  Simple, while it may share a few nodes or overlap some ways, isn't wrong, it is far easier to understand and maintain, especially for novice mappers, and ESPECIALLY when updates to imported data essentially rely on the "simple polygon" paradigm which already works so well in our map.

With respect,
SteveA
California


Douglas Hembry <[hidden email]> writes:

> Greetings everyone,
> I've just had a short changeset discussion with mapper glebius prompted
> by changeset 46612750 "Properly multipolygonize Monterey coast line". My
> understanding is that the map of this stretch of coastline has been
> restructured to avoid adjacent ways that share nodes. Accordingly, only
> a single way ever connects any set of nodes, and the single way
> participates, if necessary, in multiple relations. A result of this is
> that in a high density area like downtown Monterey Bay many small areas
> like building footprints or pedestrian areas are defined as distinct
> multipolygons, with several ways (outers) making up the outline. An
> example at:
>
> https://www.openstreetmap.org/#map=18/36.61726/-121.90045
>
> (look at Hovden Way near the top, or the outline of 700 Cannery Row,
> further down near Bubba Gump, comprised of seven outer ways)
>
> glebius believes that this approach (with the help of the reltoolbox
> JOSM plugin) is easier and less error-prone than having multiple simple
> closed ways (eg, a building footprint and an adjacent pedestrian area)
> sharing a set of nodes on their adjacent boundary. . (I hope I'm
> representing this accurately, glebius will correct me if I'm getting it
> wrong).
>
> In my limited experience I've never encountered this before, and at
> first sight I'm not convinced, particularly when considering future
> maintenance. I told glebius that I wanted to find out  what the
> community thought. Is this just one more valid optional way of mapping?
> To be recommended for adoption if possible? Or to be avoided? Thoughts?

And Rihards <[hidden email]> writes
> not an authoritative opinion : it's terrible. mapping contiguous areas
> as multipolygons results in data that is extremely hard to modify (think
> splitting landuse from a building) and is more than a minefield for newbies.
>
> personally, i either redo these as separate ways when i have the time
> (original authors do not object as they have went either mad or out of
> energy after working with multipolygons too much), or give up and leave
> the area outdated - i don't have the skills to maintain that.


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Re: Multipolygonizing

Evin Fairchild
Yeah, using multipolygons for everything is quite overkill, and it certainly does overcomplicate things, and not just for new users, but for experienced users as well. I mean, if it requires some plugin that I've never heard of in JOSM to easily edit it, then it's too complicated. I typically prefer using Potlatch 2 to edit OSM because I find JOSM to be really user-unfriendly, (I couldn't for the life of me figure out how to add a way to a relation!) so I prefer that things are kept simple as possible for idiots like me.

-Evin (compdude)

On Nov 20, 2017 9:59 AM, "OSM Volunteer stevea" <[hidden email]> wrote:
I very much agree with Douglas and Rihards that glebius' mapping is (around here) unusual, "terrible" and difficult to parse, even for experienced mappers who have been mapping for most of the history of OSM, like me.  Glebius is right in my backyard and I've found his coastal "restructurings" (e.g. http://www.osm.org/changeset/46756097) to be bizarre and unnecessary, often overwriting correct official (county GIS imported) data simply to not "share some nodes" or "improve the mess."  He claims that "the consensus in Russia is that advanced polygons is the way to go."  Well, not here, I assure both Glebuis and the talk-us list of that unequivocally.

Glebius uses a JOSM plugin (and it AMAZES him that this functionality has not yet been built into JOSM's base code!) called "reltoolbox."  It promulgates what he calls "advanced multipolygons" and in the below-noted changeset acknowledges that he believes these "became a world wide consensus," but of course, they have not.  Glebius has glibly assumed reltoolbox and its resulting data is widespread, when in fact it is not:  neither locally, regionally, nor continentally.  He further says the "quality of OSM data in USA is much worse than in other countries" when in fact, my small county of Santa Cruz (through a wiki-documented process of both importing local government landuse polygons and painfully though lovingly improving them over three revisions and many years) actually won a Gold Star Award at BestOfOSM.org for "nearly perfect landuse."  Well, before glebius snarled up a perfectly geometrically valid coastline and many of its landuse polygons, amenities, parks, marinas and recreation areas in Santa Cruz before I manually reverted a good number of his "fixes."

Glebius may believe he is "saving data" by "reducing overlapping nodes," but the added complexity to do this in multipolygons is distinctly confusing to many (most) OSM volunteers, especially beginners who find multipolygons confusing or intimidating.  I'm not saying glebius' practices or resulting data are wrong, but rather that when they overwrite perfectly already-correct data, his time is likely better spent on other OSM tasks.  Especially when he rudely calls correct and even award-winning data "a mess."

Please, glebius, don't do this here.  Everybody else in our community find your submissions to be confusing and difficult to maintain, this practice is ANYTHING BUT widespread (here in North America), you are overwriting valid data in a way that makes it nearly impossible to update with better data (especially when part of import updates) and whatever small cost you believe you are saving in either elegance or the amount of data in the map is very much outweighed by "simpler is better."  Simple, while it may share a few nodes or overlap some ways, isn't wrong, it is far easier to understand and maintain, especially for novice mappers, and ESPECIALLY when updates to imported data essentially rely on the "simple polygon" paradigm which already works so well in our map.

With respect,
SteveA
California


Douglas Hembry <[hidden email]> writes:
> Greetings everyone,
> I've just had a short changeset discussion with mapper glebius prompted
> by changeset 46612750 "Properly multipolygonize Monterey coast line". My
> understanding is that the map of this stretch of coastline has been
> restructured to avoid adjacent ways that share nodes. Accordingly, only
> a single way ever connects any set of nodes, and the single way
> participates, if necessary, in multiple relations. A result of this is
> that in a high density area like downtown Monterey Bay many small areas
> like building footprints or pedestrian areas are defined as distinct
> multipolygons, with several ways (outers) making up the outline. An
> example at:
>
> https://www.openstreetmap.org/#map=18/36.61726/-121.90045
>
> (look at Hovden Way near the top, or the outline of 700 Cannery Row,
> further down near Bubba Gump, comprised of seven outer ways)
>
> glebius believes that this approach (with the help of the reltoolbox
> JOSM plugin) is easier and less error-prone than having multiple simple
> closed ways (eg, a building footprint and an adjacent pedestrian area)
> sharing a set of nodes on their adjacent boundary. . (I hope I'm
> representing this accurately, glebius will correct me if I'm getting it
> wrong).
>
> In my limited experience I've never encountered this before, and at
> first sight I'm not convinced, particularly when considering future
> maintenance. I told glebius that I wanted to find out  what the
> community thought. Is this just one more valid optional way of mapping?
> To be recommended for adoption if possible? Or to be avoided? Thoughts?

And Rihards <[hidden email]> writes
> not an authoritative opinion : it's terrible. mapping contiguous areas
> as multipolygons results in data that is extremely hard to modify (think
> splitting landuse from a building) and is more than a minefield for newbies.
>
> personally, i either redo these as separate ways when i have the time
> (original authors do not object as they have went either mad or out of
> energy after working with multipolygons too much), or give up and leave
> the area outdated - i don't have the skills to maintain that.


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Re: Multipolygonizing

Andy Townsend
In reply to this post by stevea
On 20/11/2017 17:58, OSM Volunteer stevea wrote:
> ...  Glebius is right in my backyard and I've found his coastal "restructurings" (e.g. http://www.osm.org/changeset/46756097) to be bizarre and unnecessary, often overwriting correct official (county GIS imported) data simply to not "share some nodes" or "improve the mess."  He claims that "the consensus in Russia is that advanced polygons is the way to go."  Well, not here, I assure both Glebuis and the talk-us list of that unequivocally.

I'm not a local, just an occasional visitor to the area, but have
certainly had similar conversations with non-local mappers deciding that
(for example) a car park near me should be composed of 4 separate ways
each part of 2 or 3 multipolygons.  The thing that's in shortest supply
in OSM is mappers, and anything that prevents people from contributing
should be frowned upon.

I'm guessing he won't be reading talk-us but he does read and reply to
changeset comments, so I'd suggest commenting there on any particular
changes worth talking about.

Best Regards,

Andy


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Re: Multipolygonizing

Gleb Smirnoff-2
In reply to this post by stevea
  Hi Steve,

that was a long rant, I enjoyed reading it. Your retelling of my
words is way better than my original text, which you could quote.
I regret that I yet can't produce such a good text in English.
That's why often for me it is easier to yield rather than argue
and stand my position.

TL;DR version of my reply: I'm not going to touch OSM data in USA
anymore.

A longer version (I'll try). I assume we all agree that overlapping
or not reaching polygons where there is adjacency on the ground is
wrong. So how can we properly express adjacency? The simple way is
to run two polygons through the same subset of nodes. The advanced
is to separate this subset into a single line, which will now
belong to two multipolygons. I will try to convince you that using
advanced is easier, when it comes to "heavy" objects, like landuse=
or natural=. Imagine someone has mapped a forest, with a good
detail, precisely following its border with a farmland. Now you
want to map this farmland. In the simple way you need to follow
all nodes your predessor had drawn, clicking all the nodes, be it
25 nodes or 100. In the advanced way, you don't. You instantly
reuse his line for your new polygon. This was a most typical example
of benefits that advanced multipolygons provide.

Yes, advanced multipolygons is a professional tool, and newcomers
may find it confusing. Moreover, seasoned mappers who have spent
lot of time may in JOSM, but never encountered them, may also find
it difficult initially. Replies on this thread confirm that. But,
please, guys, don't refuse to learn something new, simply because
it is difficult! C++ is more difficult than Visual Basic, so let's
call it "terrible"? Come on, JOSM itself is difficult, but everyone
who groked JOSM, never returns to Potlach.

Look at Frederik Ramm's reply on this thread. One of the longest
term OSM contributors and member of OSMF Board supports multipolygons.
Doesn't that doubt your conviction? Try it out, before refusing it.

P.S. I know that my attempt to convince you would be as fruitless
as if I tried to convince you to use metric units :)

On Mon, Nov 20, 2017 at 09:58:53AM -0800, OSM Volunteer stevea wrote:
O> I very much agree with Douglas and Rihards that glebius' mapping is (around here) unusual, "terrible" and difficult to parse, even for experienced mappers who have been mapping for most of the history of OSM, like me.  Glebius is right in my backyard and I've found his coastal "restructurings" (e.g. http://www.osm.org/changeset/46756097) to be bizarre and unnecessary, often overwriting correct official (county GIS imported) data simply to not "share some nodes" or "improve the mess."  He claims that "the consensus in Russia is that advanced polygons is the way to go."  Well, not here, I assure both Glebuis and the talk-us list of that unequivocally.
O>
O> Glebius uses a JOSM plugin (and it AMAZES him that this functionality has not yet been built into JOSM's base code!) called "reltoolbox."  It promulgates what he calls "advanced multipolygons" and in the below-noted changeset acknowledges that he believes these "became a world wide consensus," but of course, they have not.  Glebius has glibly assumed reltoolbox and its resulting data is widespread, when in fact it is not:  neither locally, regionally, nor continentally.  He further says the "quality of OSM data in USA is much worse than in other countries" when in fact, my small county of Santa Cruz (through a wiki-documented process of both importing local government landuse polygons and painfully though lovingly improving them over three revisions and many years) actually won a Gold Star Award at BestOfOSM.org for "nearly perfect landuse."  Well, before glebius snarled up a perfectly geometrically valid coastline and many of its landuse polygons, amenities, parks, marinas and recreation areas in Santa Cruz before I manually reverted a good number of his "fixes."
O>
O> Glebius may believe he is "saving data" by "reducing overlapping nodes," but the added complexity to do this in multipolygons is distinctly confusing to many (most) OSM volunteers, especially beginners who find multipolygons confusing or intimidating.  I'm not saying glebius' practices or resulting data are wrong, but rather that when they overwrite perfectly already-correct data, his time is likely better spent on other OSM tasks.  Especially when he rudely calls correct and even award-winning data "a mess."
O>
O> Please, glebius, don't do this here.  Everybody else in our community find your submissions to be confusing and difficult to maintain, this practice is ANYTHING BUT widespread (here in North America), you are overwriting valid data in a way that makes it nearly impossible to update with better data (especially when part of import updates) and whatever small cost you believe you are saving in either elegance or the amount of data in the map is very much outweighed by "simpler is better."  Simple, while it may share a few nodes or overlap some ways, isn't wrong, it is far easier to understand and maintain, especially for novice mappers, and ESPECIALLY when updates to imported data essentially rely on the "simple polygon" paradigm which already works so well in our map.
O>
O> With respect,
O> SteveA
O> California
O>
O>
O> Douglas Hembry <[hidden email]> writes:
O> > Greetings everyone,
O> > I've just had a short changeset discussion with mapper glebius prompted
O> > by changeset 46612750 "Properly multipolygonize Monterey coast line". My
O> > understanding is that the map of this stretch of coastline has been
O> > restructured to avoid adjacent ways that share nodes. Accordingly, only
O> > a single way ever connects any set of nodes, and the single way
O> > participates, if necessary, in multiple relations. A result of this is
O> > that in a high density area like downtown Monterey Bay many small areas
O> > like building footprints or pedestrian areas are defined as distinct
O> > multipolygons, with several ways (outers) making up the outline. An
O> > example at:
O> >
O> > https://www.openstreetmap.org/#map=18/36.61726/-121.90045
O> >
O> > (look at Hovden Way near the top, or the outline of 700 Cannery Row,
O> > further down near Bubba Gump, comprised of seven outer ways)
O> >
O> > glebius believes that this approach (with the help of the reltoolbox
O> > JOSM plugin) is easier and less error-prone than having multiple simple
O> > closed ways (eg, a building footprint and an adjacent pedestrian area)
O> > sharing a set of nodes on their adjacent boundary. . (I hope I'm
O> > representing this accurately, glebius will correct me if I'm getting it
O> > wrong).
O> >
O> > In my limited experience I've never encountered this before, and at
O> > first sight I'm not convinced, particularly when considering future
O> > maintenance. I told glebius that I wanted to find out  what the
O> > community thought. Is this just one more valid optional way of mapping?
O> > To be recommended for adoption if possible? Or to be avoided? Thoughts?
O>
O> And Rihards <[hidden email]> writes
O> > not an authoritative opinion : it's terrible. mapping contiguous areas
O> > as multipolygons results in data that is extremely hard to modify (think
O> > splitting landuse from a building) and is more than a minefield for newbies.
O> >
O> > personally, i either redo these as separate ways when i have the time
O> > (original authors do not object as they have went either mad or out of
O> > energy after working with multipolygons too much), or give up and leave
O> > the area outdated - i don't have the skills to maintain that.
O>
O>

--
Gleb Smirnoff

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Re: Multipolygonizing

Mark Wagner
In reply to this post by Evin Fairchild
On Mon, 20 Nov 2017 10:15:01 -0800
Evin Fairchild <[hidden email]> wrote:

> (I couldn't for the life of  me figure out how to add a way to a
> relation!)

Select a way currently part of the relation.  Shift-click on the way
you want to add.  Select "Update multipolygon" from the "Tools" menu,
or hit Ctrl+Shift+B.  Simple.

Of course, this only works for ordinary relations.  If the way you
clicked on is shared by two or more relations, you need to go
through the far more complicated method of playing with the
relation-editor dialog.

--
Mark

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Re: Multipolygonizing

Mike N.
In reply to this post by Gleb Smirnoff-2
On 11/20/2017 2:36 PM, Gleb Smirnoff wrote:
> In the simple way you need to follow
> all nodes your predessor had drawn, clicking all the nodes, be it
> 25 nodes or 100. In the advanced way, you don't. You instantly
> reuse his line for your new polygon. This was a most typical example
> of benefits that advanced multipolygons provide.

   This is a good example where multipolygons make sense.   I have run
into this in the past and naturally migrated to a multipolygon instead
of clicking through hundreds of nodes.

   However for smaller landuse areas such as residential neighborhoods
or shopping centers, there may be only 4-20 nodes per adjacent polygon.
  For those cases, I find that multipolygons only increase the load on
future maintenance and present a major confusion factor for new users.

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Re: Multipolygonizing

Joel Holdsworth
In reply to this post by Gleb Smirnoff-2

>
> A longer version (I'll try). I assume we all agree that overlapping
> or not reaching polygons where there is adjacency on the ground is
> wrong. So how can we properly express adjacency? The simple way is
> to run two polygons through the same subset of nodes. The advanced
> is to separate this subset into a single line, which will now
> belong to two multipolygons. I will try to convince you that using
> advanced is easier, when it comes to "heavy" objects, like landuse=
> or natural=. Imagine someone has mapped a forest, with a good
> detail, precisely following its border with a farmland. Now you
> want to map this farmland. In the simple way you need to follow
> all nodes your predessor had drawn, clicking all the nodes, be it
> 25 nodes or 100. In the advanced way, you don't. You instantly
> reuse his line for your new polygon. This was a most typical example
> of benefits that advanced multipolygons provide.
>


I use them for this all the time.

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Re: Multipolygonizing

stevea
In reply to this post by stevea
On Nov 20, 2017, at 11:32 AM, Gleb Smirnoff <[hidden email]> wrote:
>  Hi Steve,
> that was a long rant, I enjoyed reading it.

Thank you, but I'd call it "moderate length" for me, I can and do (infamously) rant MUCH longer, as many will attest.

> Your retelling of my
> words is way better than my original text, which you could quote.
> I regret that I yet can't produce such a good text in English.
> That's why often for me it is easier to yield rather than argue
> and stand my position.

I did quote (in several place) your original words, so I'm not sure what your point is here, apologies for my confusion.

We must use SOME language to communicate, and while this is talk-us, (and the USA has no official language, but English IS widely used), we use English.  I am multilingual, but as English is my native tongue, I prefer it to Polish, Hungarian, French or Spanish, as I wouldn't be anywhere near as fluent.  Regrets I am unable to converse with you in Russian.  Your English seems quite fluent to me, I encourage you to continue the conversation as best you might without feeling the need to simply yield because of your language skills, you write quite well (believes this user of English).

> TL;DR version of my reply: I'm not going to touch OSM data in USA
> anymore.

I am disappointed you would take so extreme a stance, as I wish to see quality edits done by quality editors to increase OSM's quality, and you can and do perform such edits.  What many here are asking you to do is to tone down or stop with the "multipolygonization" that you do so much of, especially as it changes existing and correct data (simple polygons, sometimes as part of an import of official data).  Many agree there simply is no need to do this.  Existing, correct, (sometimes imported) polygons are important to keep updated when needed, but this becomes difficult after your multipolygonization process.  Especially as it uses a JOSM plug-in which while you are clearly facile at using, is not at all widespread in the USA.  The process of multipolygonization is understood, especially by more technically advanced and seasoned OSM editors, but it is the process of CONVERTING existing polygons to multipolygons on a widespread basis where it seems there is no good reason for this to occur (and indeed even frustrates import updates).  This is what we are asking you not to do (so much of).

Again, I agree that the end-result of your data is technically correct, and indeed it makes sense to do this "sharing of ways" in certain use cases (we can both cite many examples — I have certainly done this myself in places).  But to go to (especially imported) existing data and rework them into much more complex structures when their simplicity is both sufficient and correct seems not only a waste of your good time and editing skills, it makes it difficult for others.

> A longer version (I'll try). I assume we all agree that overlapping
> or not reaching polygons where there is adjacency on the ground is
> wrong.

"Not-reaching," meaning they create small gaps or "gores," yes, those polygons are technically wrong.  Polygons with overlapping ways, even where they share nodes (and even if they don't share nodes), no, those are not wrong.  You may believe that these are "sloppy" or have superfluous data, and you may even prefer your multipolygon approach, but what that does is replaces simple and correct data with complex and correct data.  I and others here see little point in doing that, especially as it frustrates beginners and complicates import updates.

> So how can we properly express adjacency?<redacted for brevity>

We know.  We agree.  We simply don't think this is a good idea to go and do this on existing data (on a medium- or large-scale, as you and your JOSM plugin do) where to do so simply isn't needed, and indeed complicates further data editing.

> Yes, advanced multipolygons is a professional tool, and newcomers
> may find it confusing. Moreover, seasoned mappers who have spent
> lot of time may in JOSM, but never encountered them, may also find
> it difficult initially. Replies on this thread confirm that. But,
> please, guys, don't refuse to learn something new, simply because
> it is difficult! C++ is more difficult than Visual Basic, so let's
> call it "terrible"? Come on, JOSM itself is difficult, but everyone
> who groked JOSM, never returns to Potlach.

We are not refusing to learn this.  We agree your method of data entry is valid, as we do it (as Frederik so excellently offers us an example) as well, WHERE IT IS WARRANTED TO DO SO.  And, THAT IS NOT EVERYWHERE.

> Look at Frederik Ramm's reply on this thread. One of the longest
> term OSM contributors and member of OSMF Board supports multipolygons.
> Doesn't that doubt your conviction? Try it out, before refusing it.

I have entered and edited thousands of OSM multipolygons:  I and many others are are not "against them."  What we are asking is that you not "convert" existing, simple (sometimes imported) polygon data into multipolygon data for no particular good reason, except that you have a JOSM plugin and decide to use it on a relatively large scale.  I humbly submit to you, sir, that your good editing skills are much better spent on other, more important tasks, ones with less confusing results.  Again, please don't misunderstand me:  I wish our editors (both software and people) were better users of multipolygons, as they are quite useful, and indeed there are certain things which are impossible without them.  Unfortunately, our editors (software and people) are not as facile with multipolygons as we would like.  This will improve with time.  In the meantime, let's agree that polygons are also correct data structures to use, and indeed are sometimes even preferred (as with imports).  They are not wrong, they are not sloppy, they might use a bit more data, but to many, they are preferred.  It is possible for more than one style of data to represent accurately the truth on the ground.

> P.S. I know that my attempt to convince you would be as fruitless
> as if I tried to convince you to use metric units :)

I am one of the most metric system-using people in the USA that I know, I started being metric in the 1970s.  Please, making such assumptions is fraught with peril.  Let us not assume about each other, it makes for a better dialog and project in the long-term.

Gleb, I signed my missive "with respect" as I do respect your editing.  As members of this project, we do offer respect to one another:  look at how generous Douglas was with you as he greatly extended himself to better and fully understand your approach in his changeset comments.  I hope the message you hear is that we wish you to continue making good contributions to OSM, including in North America and USA.  And also, that you hear many of us as we say "please, Gleb, ease up on the over-multipolygonization of existing data, especially as their polygons may be part of imports."  Yes, it can be hard to know which data are imported and which are not.  Yes, it can be hard to know when data should be "properly" multipolygonized and when not.  We only ask that you listen and consider, and it looks like you have and do.

Thank you,
SteveA
California
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Re: Multipolygonizing

Gleb Smirnoff-2
In reply to this post by Mark Wagner
On Mon, Nov 20, 2017 at 11:43:34AM -0800, Mark Wagner wrote:
M> > (I couldn't for the life of  me figure out how to add a way to a
M> > relation!)
M>
M> Select a way currently part of the relation.  Shift-click on the way
M> you want to add.  Select "Update multipolygon" from the "Tools" menu,
M> or hit Ctrl+Shift+B.  Simple.
M>
M> Of course, this only works for ordinary relations.  If the way you
M> clicked on is shared by two or more relations, you need to go
M> through the far more complicated method of playing with the
M> relation-editor dialog.

Or use "reltoolbox" plugin, where there is a notion of current                                                  
relation, and while you got your relation selected as current,                                                  
adding or removing objects to it is clicking "+" or "-" icon on                                                  
the sidebar, having object selected. For multipolygons it will also                                              
set "outer" or "inner" role automatically.              

--
Gleb Smirnoff

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Re: Multipolygonizing

Kevin Kenny-4
In reply to this post by Gleb Smirnoff-2
I'm somewhat relieved to hear Gleb and Frederik injecting a voice
indicating that 'shared ways' separating regions might be an
acceptable approach, because I've adopted it myself. Well, to some
extent, any way.

I'm generally against sharing ways EXCEPT when topology demands it -as
it often does. It's pretty nonsensical to start going to shared ways
just because a building abuts a parking field, for instance.

Still, if two adjacent polygons are the same sort of thing, or
specifically defined to be conterminous, then I certainly want to
share the boundary. By the "same sort of thing," I mean administrative
regions that share a boundary, or different land uses (following our
presumption that a piece of land has only one land use), or different
types of land cover (including water). And 'specifically defined to be
coterminous' includes things like parks that stop at a waterfront.

I would tend to avoid shared ways for things like a wood that stops at
the boundary line of a protected area. The trees don't know where the
boundary is, and the boundary won't move if the adjacent landowner
allows his plot to go back to nature.

There are several reasons for shared ways between topologically adjacent areas.

(1) Data consistency. This is the primary reason. As Gleb points out,
if a shared boundary is a single way, there's no chance that someone
will retrace the boundary of one of the neighbouring regions without
retracing the other, or will enter them inconsistently in the first
place.

(2) Rendering. We've already discovered for boundary=administrative
that representing bordering regions as separate polygons sharing only
nodes rules out using things like dashed-line rendering, because each
boundary will be rendered twice, and there is nothing to ensure that
the dashes will be in the same relative phase; dashed lines tend to
turn into solid lines in such a scheme. That's one of several reasons
that we have tried to keep shared ways on all boundary=administrative
meshes. I foresee in the future (and already confront in my own
rendering) cases where protected areas, or even things like
leisure=park, are rendered similarly and therefore need shared ways to
get a clear display.

(3) Ease of editing (for better-informed or better-tooled users). At
least for me, working in JOSM, I find updating a mesh of multipolygons
with shared ways to be fairly straightforward. Split the ways at any
new corners, draw any new ways, update the touching regions, delete
any obsolete ways. Sure, it's a different workflow than the one for
simple polygons, but for that workflow, I find myself retracing over
long sets of points, or else splitting, duplicating, reversing and
rejoining ways. The duplicated ways are difficult to work with, since
they share all the points, and I have to puzzle over some pretty
subtle things to understand which copy I'm working with. By contrast,
the split and joined ways in a shared-ways structure always have
distinct geometry.

By contrast, the chief argument against multipolygons is that they are
unfriendly to newcomers.  I'll happily concede this point in part.
They certainly demand a somewhat deeper understanding of the data
model, and the newcomer-friendly tools such as Potlatch don't really
do them competently. This argument is stronger that Gleb and Frederik
appear to recognize. Given the difficulty of recruiting mappers, we
surely want to make life as easy as possible for newbies, even if that
comes at some expense in the ease of use for the old hands.

That said, how likely is a newcomer to be editing a complex mesh of
land use or land cover and not mess up the topology, however it's
represented? I suspect that new mappers attempting to adjust these
features will always wind up creating overlaps, gores and broken
multipolygons. (SOME multipolygons are unavoidable because areas have
enclaves or exclaves!) Moreover, part of the newcomer-unfriendliness
comes from the fact that examples of shared ways are sparse, and tend
to be on stable things like administrative regions, the shorelines of
large waterbodies, and similar features that newcomers are
(rightfully) a little afraid to edit in the first place.  Heck, how
many newcomers will even recognize that topology is important?

I may have a somewhat warped view of things. I got into using shared
ways when tidying conflicting imports of various public lands in New
York State, where there were many gores among county and township
lines, shorelines, and the boundaries of various sorts of protected
area. The boundaries are topologically complex, and being constrained
to deal with them by retracing partial ways would be a nightmare.
Shared ways was really the only approach that worked, and from what I
hear, for complex cases, it's still considered acceptable. That's a
relief!

Once I became fluent with the approach of using shared ways, I've come
to use it when, for instance, adding landcover or land use polygons
even in my own neighbourhood. Even there, it could be that the use is
noncontroversial, since I live in a hilly area and as a consequence,
most of the polygons have edges that twist and turn. Nevertheless, I
freely concede that I may have overused the approach.

I surely don't see a compelling reason to adopt any proposal to use
mechanical edits to replace polygons that share two or more nodes with
a multipolygon mesh. I'll presume that the mappers who entered the
polygons had their own reasons for entering the data as they did. But
I do feel free to introduce shared ways when editing such a beast,
because I struggle with keeping the topology consistent otherwise.

As long as people don't start to claim that the approach of using
shared ways is invalid, or that I'm committing vandalism by adopting
them when I'm either entering new data or editing adjacent polygons
for other reasons, I'm content.

And I do consider it unacceptable when someone removes a shared border
for which I've carefully curated a consensus solution from multiple
conflicting data sources, and replaces it with a simple polygon that
fails to align with anything along its margins. (I've recently sent
rather a long laundry list of problems to a mapper who did just that.
No response yet.) Introducing incorrect data in order to make the
format more friendly to newcomers is not the way to move forward.

We should strive to make simple things easy. But perhaps more
importantly, we need to continue making difficult things possible.

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Re: Multipolygonizing

stevea
In reply to this post by Doug Hembry
Thank you, Kevin for your thoughtful and rather complete reply!

Mark Wagner <[hidden email]> wrote:
> Of course, this only works for ordinary relations.  If the way you
> clicked on is shared by two or more relations, you need to go
> through the far more complicated method of playing with the
> relation-editor dialog.

It is no secret that using either iD or Potlatch for relation editing is difficult and error-prone, nigh unto impossible for novice editors to either understand or perform easily.  By contrast, while it does take some practice to learn, I find JOSM's relation editor to be a straightforward method to edit OSM relations.  In short, the "four pane dialog" (not strictly correct, but it pedagogically suffices) consists of "key-value pairs on top, (left and right); member elements and selections on bottom (left and right)."  Along with the buttons to the left of and between the bottom two panes (sort, reverse, select, move, ...), you have all you need to edit relations.  This is a modeless (not modal) dialog, meaning that while the relation editing window is open, selections (e.g. click, drag a selection box...) and operations (e.g. split or join...) can/should be performed on underlying data in the geography editing window.  Taken together, these are the seeds of learning how to effectively edit relations in JOSM.

Plug-ins that offer "power tools" beyond that?  Well, caveat usor.

I wholeheartedly agree with much said in this thread:  both polygons and multipolygons are perfectly valid data structures to use in cases where choosing one or the other is a matter of taste, preference, use-case, or all three.  (Some uses absolutely require multipolygons, and that is that, other uses offer a choice of polygons OR multipolygons, where one or the other are equally correct).  Notwithstanding JOSM's current paradigm noted above, our tools have a ways to go before they present simple methods to edit relations (type multipolygon or others) so that all and sundry are comfortable editing them.  OSM gets better at this, though it is taking some time to get there.

I believe a most important result from this thread is that there are many use cases where either polygons OR multipolygons are correct.  Really, we are not very far apart from rather fully agreeing with one another.

SteveA
California
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Re: Multipolygonizing

Gleb Smirnoff-2
In reply to this post by stevea
   Steve,

On Mon, Nov 20, 2017 at 12:23:53PM -0800, OSM Volunteer stevea wrote:
O> I did quote (in several place) your original words, so I'm not sure what your point is here, apologies for my confusion.
O>
O> We must use SOME language to communicate, and while this is talk-us, (and the USA has no official language, but English IS widely used), we use English.  I am multilingual, but as English is my native tongue, I prefer it to Polish, Hungarian, French or Spanish, as I wouldn't be anywhere near as fluent.  Regrets I am unable to converse with you in Russian.  Your English seems quite fluent to me, I encourage you to continue the conversation as best you might without feeling the need to simply yield because of your language skills, you write quite well (believes this user of English).

Of course I am not suggesting to use other language in US :) I just explained,
that as a discussion follows technical context, I am closely to par with native
speakers. But as it falls off, I really can't produce good texts. Writing the
previous reply took nearly an hour of my time! :) The other option was "screw
it up guys, I'm going home", which is yield and abandon these and future edits.

And retelling someone's words really makes different to quoting them. Even
without an explicit manipulation of sense the connotation changes.

Ok, let's get back on topic.

Looks like the acception of multipolygons here is not as bad as I initially
read in this email thread. So, we agree that at some level they are easier
to maintain that shared nodes. Do we?

Of course multipolygonizing couple of buildings that touch coastline in
Monterey was wrong. Sorry, I was in a multipolygonizing rage as I was
going through the coastline. :)

But the rest of the coastline? The nodes can be shared by any of:
1) coastline, 2) beach 3) county & state borders 4) marine preserve.
And there are ten's of thousands of nodes, because this is a natural
crazy curved line. This is the most clear example of where multipolygons
are way easier to draw and maintain than running multiple lines through
the same set of nodes!

O> ... it is the process of CONVERTING existing polygons to multipolygons on a widespread basis where it seems there is no good reason for this to occur (and indeed even frustrates import updates).  This is what we are asking you not to do (so much of).

Well, OSM started in 2006 and support for advanced multipolygons appeared
in 2011 (correct me if I am wrong). So, at time they came in there were
already fairly enough data in the database. Should we treat OSM as "write
only" database? E.g. we only add data, but don't improve already entered?
The advanced multipolygons appeared because there was a demand for them,
so why not use them for existing data, if resulting product becomes better?

Now, for the import updates. Here I am starting to understand the strong
pushback against my edits. Import updates is something I never heard
about! Please tell me more about that. Because in all other places that
I have edited (Russia, Ukraine, Georgia) imports were treated as something
that comes in once, and then is adopted into OSM. Do I understand you
correct that here you got recurring imports, where the import script needs
to find the object it created previously and edit it? Shoudn't this object
be protected then? At least a tag note="DO NOT EDIT ME"?

O> > A longer version (I'll try). I assume we all agree that overlapping
O> > or not reaching polygons where there is adjacency on the ground is
O> > wrong.
O>
O> "Not-reaching," meaning they create small gaps or "gores," yes, those polygons are technically wrong.  Polygons with overlapping ways, even where they share nodes (and even if they don't share nodes), no, those are not wrong.  You may believe that these are "sloppy" or have superfluous data, and you may even prefer your multipolygon approach, but what that does is replaces simple and correct data with complex and correct data.  I and others here see little point in doing that, especially as it frustrates beginners and complicates import updates.

Actually by overlapping I meant polygons with non-zero shared surface.
I still assume you agree that this is wrong.

Those that share ways, or share nodes, or use different nodes with
exactly same coordinates, aren't overlapping, they are adjacent. Yes,
they are technically correct! However, maintaining them is a hell.
If you want to create an object that reuses already existing curves
in the database, you need to do a lot of click-job.

O> > So how can we properly express adjacency?<redacted for brevity>
O>
O> We know.  We agree.  We simply don't think this is a good idea to go and do this on existing data (on a medium- or large-scale, as you and your JOSM plugin do) where to do so simply isn't needed, and indeed complicates further data editing.

I still stand that it makes easier further data editing. :(

All these coastline multipolygonizing was prerequisite to importing
State Marine Reserves. And indeed after preparations adding SMR
boundaries was 100x times easier. Here is example changeset of
adding a couple of SMRs once coastline is multipolygon:

http://www.openstreetmap.org/changeset/47115827

How small and concise it is! And if next year Department of Wildlife
will announce a new one, adding it would be again a minute task.

O> ... In the meantime, let's agree that polygons are also correct data structures to use, and indeed are sometimes even preferred (as with imports).  They are not wrong, they are not sloppy, they might use a bit more data, but to many, they are preferred.  It is possible for more than one style of data to represent accurately the truth on the ground.

Sure, I don't claim that polygons are incorrect. I just find out that
at some level of map detail and fullness they are much more difficult
to maintain than advanced multipolygons. Yes, I mistakenly assumed
that everyone is familiar with the reltoolbox plugin, which is an
important part of making multipolygons easier.

Here is example, please open the area around this meadow in JOSM:

http://www.openstreetmap.org/relation/5926445#map=15/55.8569/37.2520

Just browse around in JOSM and try to do edits without committing them.
Add imaginary natural preserve there, or a military closed area. Or imagine
you want to go to higher detail, so you want to split existing forest into
a forest and a scrub. Anything that follows existing lines, can be instantly
added, with as much clicks as there are _lines_ in the boundary. Lines, not
nodes!

Compare that area to what we have around Santa Cruz. Imagine we could do
it better :)

O> Gleb, I signed my missive "with respect" as I do respect your editing.  As members of this project, we do offer respect to one another:  look at how generous Douglas was with you as he greatly extended himself to better and fully understand your approach in his changeset comments.  I hope the message you hear is that we wish you to continue making good contributions to OSM, including in North America and USA.  And also, that you hear many of us as we say "please, Gleb, ease up on the over-multipolygonization of existing data, especially as their polygons may be part of imports."  Yes, it can be hard to know which data are imported and which are not.  Yes, it can be hard to know when data should be "properly" multipolygonized and when not.  We only ask that you listen and consider, and it looks like you have and do.

I'm open to listen and learn about updated imports. Let's see how bad is
my damage, can it be resolved and how we can try to coexist the advanced
map management with imports.

--
Gleb Smirnoff

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Re: Multipolygonizing

Gleb Smirnoff-2
In reply to this post by stevea
On Mon, Nov 20, 2017 at 02:13:44PM -0800, OSM Volunteer stevea wrote:
O> Plug-ins that offer "power tools" beyond that?  Well, caveat usor.

Note that a large part of current JOSM base functionality before was
in plugins. So, doesn't make sense to diminish some tool because it
isn't in base. Whether some code goes into JOSM or stays as plugin is
driven by two things: 1) number of plugin users 2) willingness of plugin
author to yield his code to JOSM repo, meaning disown his code. And
for many people that also means lose commit access to their code.

--
Gleb Smirnoff

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Re: Multipolygonizing

stevea
In reply to this post by stevea
Kevin and others:  please do not misunderstand me.  There ARE times when shared ways between multipolygons is an elegant and THE correct solution, as you, I and many others have found to be true and edited into existence many times.  By no means do I advocate that where such beauty has been completed that it be torn apart and reverted to simple polygons, that would be a giant step backwards.  These solutions are NOT "too complicated," and it is a misunderstanding of what I have been saying in this thread to think so.

Your statement that "mechanical edits (often by the JOSM tool reltoolbox) running roughshod over carefully curated data" strikes at the bullseye of what I wish to convey.  Such trampling really makes updating imported (curated) data quite difficult, and OSM really DOES want to encourage the updating of imported data.  I AM saying:  please BE CAREFUL multipolygonizing polygons, especially where tagging or changeset data might indicate they are part of an import or a curated set of data.

It may be that as other geodata, especially those which align well with the idea that "shared ways are a good idea in these data," become better aligned with OSM's multipolygon data structure, this situation greatly improves.  Now, there is some alignment, though it is not perfect; for example, shapefile data imported into JOSM are either "OK after import" or "come close enough to easily fix" (in my opinion).  But concomitant with this is that OSM editors — software, novices, intermediates and experts alike — not be afraid of or intimidated by relations and/or multipolygons (and editing them).  While our "primitive types" of nodes and ways are relatively easy to learn, relations are not, but we MUST prioritize it as an important task that even beginning users better familiarize themselves and gain comfort with these more complex types of data — early, and often.

Please, ENTER data using shared ways where it makes sense to do so.  Nobody is saying "don't do that."  ALSO, please be aware that existing NON-multipolygon data (especially imports and other "curated" data) may very well suffer from the process of being "multipolygonized."  There is a balance to be struck, and I would be very disheartened to see our map become "dumbed down" by data which should be multipolygon somehow become twisted into not.

SteveA
California

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Re: Multipolygonizing

Gleb Smirnoff-2
In reply to this post by Kevin Kenny-4
  Kevin,

On Mon, Nov 20, 2017 at 04:29:56PM -0500, Kevin Kenny wrote:
K> (3) Ease of editing (for better-informed or better-tooled users). At
K> least for me, working in JOSM, I find updating a mesh of multipolygons
K> with shared ways to be fairly straightforward. Split the ways at any
K> new corners, draw any new ways, update the touching regions, delete
K> any obsolete ways. Sure, it's a different workflow than the one for
K> simple polygons, but for that workflow, I find myself retracing over
K> long sets of points, or else splitting, duplicating, reversing and
K> rejoining ways. The duplicated ways are difficult to work with, since
K> they share all the points, and I have to puzzle over some pretty
K> subtle things to understand which copy I'm working with. By contrast,
K> the split and joined ways in a shared-ways structure always have
K> distinct geometry.

Thanks for this paragraph! This was text that was right on my tongue,
but I failed to wordsmith it properly.

--
Gleb Smirnoff

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Re: Multipolygonizing

Andy Townsend
In reply to this post by Gleb Smirnoff-2
On 20/11/2017 19:36, Gleb Smirnoff wrote:
> Come on, JOSM itself is difficult, but everyone
> who groked JOSM, never returns to Potlach.

Untrue.  Each of the OSM editors has strengths and weaknesses - it's
simply a case of finding the best tool for the job.  In some cases that
might be JOSM; in some cases it might be something completely different
(StreetComplete?).  JOSM isn't the best at everything - it has a user
interface out of the fifth circle of hell and seems intent on dragging
the user straight back there.  It fails with some stuff that is "basic"
to e.g. Potlatch (mapping with waypoints recorded with information in
them as you go for example).  See questions such as
https://help.openstreetmap.org/questions/7675/josm-is-it-possible-to-convert-an-individual-waypoint-in-a-gpx-file-to-a-node 
for a bit more discussion on that.

Best Regards,
Andy


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