Re: [Talk-us] Multipolygonizing
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as they have went either mad or out of energy after working with multipolygons too much), or give up and leave the area outdated - i don't have the skills to maintain that.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 ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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). ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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 frede...@remote.org ## N49°00'09" E008°23'33" ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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 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 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
Re: [Talk-us] Multipolygonizing
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" 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 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 h
Re: [Talk-us] Multipolygonizing
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 ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
On Mon, 20 Nov 2017 10:15:01 -0800 Evin Fairchild 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 ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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
Re: [Talk-us] Multipolygonizing
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. ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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. ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
On Nov 20, 2017, at 11:32 AM, Gleb Smirnoff 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? 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,
Re: [Talk-us] Multipolygonizing
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 ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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 coul
Re: [Talk-us] Multipolygonizing
Thank you, Kevin for your thoughtful and rather complete reply! Mark Wagner 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 ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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? 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 Reserv
Re: [Talk-us] Multipolygonizing
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 ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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 ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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 ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
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 ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
Hi everybody! Please remember to stay on topic and friendly. This thread seems to be drifting off into a discussion about the merits of OSM editors. Also remember that long replies tend to result in people talking past one another. Short, sweet, and to the point helps a conversation stay on topic. -Ian Your friendly talk-us moderator On Mon, Nov 20, 2017 at 5:24 PM, Andy Townsend wrote: > 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 > > > ___ > Talk-us mailing list > Talk-us@openstreetmap.org > https://lists.openstreetmap.org/listinfo/talk-us > ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
On Mon, Nov 20, 2017 at 6:15 PM, OSM Volunteer stevea wrote: > 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. The cases where I have intentionally converted curated, imported data to shared ways have all been in imports that I curate myself. I wind up treating the result as being no different as any other imported object that's subsequently been modified by a local mapper. If a reimport discovers that the last user to touch the object wasn't the import user ID, it flags the upstream data for manual conflation, and does nothing. Even when it does find that it was the last modifier of the object, the most it does is to prime JOSM with the proposed change and let me confirm and commit. The largest data set that I work with has a couple of thousand polygons. I've done two reimports, each of which have changed a couple of dozen. Of those, a handful, few enough to count on fingers, have been subsequently modified by local mappers. While the initial import ran over a couple of months, an annual reimport takes me maybe a couple of evenings. Yes, I did hear a sentiment calling for "dumbing down" the map - and it wasn't so much you specifically, as that the early returns appeared to be shaping up into yet another Europe-North America divide. I know that your position is considerably more subtle; we've discussed this one fairly extensively already. I just really want to nip the idea in the bud that simplicity is preferable to correctness. I'm also fairly cross, because I've discovered in the last week that two large multipolygon relations that I had spent hours on setting up had been dismembered. Since they were born in an import (however much manual editing and conflation was done), I'm not comfortable with restoring the data, even though significant information has been lost by the manual changes. In both cases, the topology was damaged by the Potlatch user, who then 'repaired' things by moving tagging that had been on the relation to some, but not all, of the outer ways of the modified object. These were two different users. I suppose this reinforces both the case that multipolygons should be used only as a last resort and that imports damage the community, but I'm sad to see regions of the map lose tagging that had previously been informative, and begin to feel that my hands are tied from repairing them. ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
Briefly (thanks for the reminder, again, Ian!): If the reltoolbox plug-in as as powerful as I am beginning to understand it may be (I appreciate the introduction, Gleb), and given my agreement that certain use cases (especially landuse) benefit greatly from multipolygonized boundaries (they do), I actually CAN imagine that the SCCGIS V4 landuse import data (in 2019 or 2020) could become multipolygon. This likely would involve a pre-upload translation of polygon data into mulitipolygon using the tool, then conflation (which has to be done anyway). Except, we upload multipolygons as we delete existing polygons during the conflation-and-upload phase. I wanted to offer that bright spot of hope to anybody's lingering beliefs that I am "mule-entrenched" in my beliefs that existing polygons are always superior. They are not. They make updates harder, but I think I can get over that, as I can be convinced that "once done, the time investment is worth it" for the future benefits that multipolygons bring. SteveA California ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
Gleb, On 11/21/2017 12:02 AM, Gleb Smirnoff wrote: > 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. :) We have a general (unwritten) convention in OSM and that is "don't force your taste on other mappers". When you edit data contributed by others, and you improve it with your own knowledge or data collected on the ground, then nobody expects any restraint from you - improve away! However, in matters of taste - where you are NOT adding information, and instead just changing the represenation of the data in the database - we tend to say: It is for you to decide the style in which YOU contribute, but do not try to overrule others and force your style on them. (There's another issue that mappers never agree on, and that's whether when there's a track on the edge of the forest and beyond that, a meadow, all three should share nodes, or whether room is to be left to the left and right of the track because "the forest doesn't end in the middle of the track"). These things are matters of taste, and neither representation is more correct or contains more information than the other; two stubborn mappers at loggerheads could potentially re-style an area from one style to the other and back every week. Hence: Apply your personal style to new contributions that you make, but don't go around applying it to contibutions made by others. This sort of "cleanup" benefits few but your personal sense of orderliness, and your time is better spent actually improving data instead of just fiddling with how the same data is represented in the database. Bye Frederik -- Frederik Ramm ## eMail frede...@remote.org ## N49°00'09" E008°23'33" ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
Steve, On Mon, Nov 20, 2017 at 04:34:18PM -0800, OSM Volunteer stevea wrote: O> If the reltoolbox plug-in as as powerful as I am beginning to understand it may be (I appreciate the introduction, Gleb), and given my agreement that certain use cases (especially landuse) benefit greatly from multipolygonized boundaries (they do), I actually CAN imagine that the SCCGIS V4 landuse import data (in 2019 or 2020) could become multipolygon. This likely would involve a pre-upload translation of polygon data into mulitipolygon using the tool, then conflation (which has to be done anyway). Except, we upload multipolygons as we delete existing polygons during the conflation-and-upload phase. O> O> I wanted to offer that bright spot of hope to anybody's lingering beliefs that I am "mule-entrenched" in my beliefs that existing polygons are always superior. They are not. They make updates harder, but I think I can get over that, as I can be convinced that "once done, the time investment is worth it" for the future benefits that multipolygons bring. Okay, I will withhold myself from touching polygons in the Santa Cruz County for next couple of years, and let's see how your future experience with SCCGIS goes on. We can get back to this question later in scope of Santa Cruz. Meanwhile, do I understand that my initial understanding of strong consensus against multipolygons in the USA overall was wrong reading? First few emails in the thread made me think so. I'd like to continue working on coastline, and map all remaining SMRs and later maintain them. I also want keep using multipolygons in any regular edits. Are there any objections? -- Gleb Smirnoff ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
On 21/11/17 14:29, Gleb Smirnoff wrote: Steve, On Mon, Nov 20, 2017 at 04:34:18PM -0800, OSM Volunteer stevea wrote: O> If the reltoolbox plug-in as as powerful as I am beginning to understand it may be (I appreciate the introduction, Gleb), and given my agreement that certain use cases (especially landuse) benefit greatly from multipolygonized boundaries (they do), I actually CAN imagine that the SCCGIS V4 landuse import data (in 2019 or 2020) could become multipolygon. This likely would involve a pre-upload translation of polygon data into mulitipolygon using the tool, then conflation (which has to be done anyway). Except, we upload multipolygons as we delete existing polygons during the conflation-and-upload phase. O> O> I wanted to offer that bright spot of hope to anybody's lingering beliefs that I am "mule-entrenched" in my beliefs that existing polygons are always superior. They are not. They make updates harder, but I think I can get over that, as I can be convinced that "once done, the time investment is worth it" for the future benefits that multipolygons bring. Okay, I will withhold myself from touching polygons in the Santa Cruz County for next couple of years, and let's see how your future experience with SCCGIS goes on. We can get back to this question later in scope of Santa Cruz. Meanwhile, do I understand that my initial understanding of strong consensus against multipolygons in the USA overall was wrong reading? First few emails in the thread made me think so. I'd like to continue working on coastline, and map all remaining SMRs and later maintain them. I also want keep using multipolygons in any regular edits. Are there any objections? I use multipolygons extensively for the land cover around Rocky Mountain National Park. ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
On Nov 21, 2017, at 1:27 PM, Gleb Smirnoff wrote: > Okay, I will withhold myself from touching polygons in the Santa Cruz County > for next couple of years, and let's see how your future experience with > SCCGIS goes on. We can get back to this question later in scope of Santa Cruz. This is a very happy result, thank you for the good (if rather public in talk-us) dialog. I think it was beneficial to the greater OSM community that our dialog was so public, as Kevin and I have been discussing "shared ways in multipolygons vs. regular polygons" off-list for some time, and I've always known this trend towards "shared ways" would deeply affect a large import I keep updated in my county. I believe this topic has made other OSM importers/maintainers of mostly- or exclusively-polygon data wonder what the best course of action is as OSM evolves to "shared ways" becoming more and more common. I hope it has helped a better consensus to emerge – it feels like it is doing so locally. What is emerging (at least here, between me and Gleb) is that there will come a point in either initial/original imports that are largely or exclusively polygon-only when it simple becomes time to "bite the bullet" and do the initial work to convert these to multipolygon as the trend towards "shared ways" grows. Yes, that is lots of work up front, but I believe in advance that it will be worth it in the editing time/efforts saved in the future as Gleb and Kevin have pointed out its many editing benefits. (I agree it is easier to maintain such "edges," boundaries especially, including landuse, which are "shared ways" as multipolygons allow us to do. EXCEPT in large, existing imports!). > Meanwhile, do I understand that my initial understanding of strong consensus > against multipolygons in the USA overall was wrong reading? First few emails > in the thread made me think so. Gleb, it was a sort of misunderstanding, and it doesn't seem important to lay blame on anybody in particular. What is important is that we seem to agree that while polygons certainly have their place and aren't going away, multipolygons are here to stay as well, and there is a distinct trend towards using them in a "shared way" context where it makes sense to do so. (The good examples that Kevin listed, likely more). Yes, as Frederik said, it can be a matter of taste which is better, as both are correct (one is harder to edit in one context, the other is harder to edit in another context), and so we should not be spending time "converting" from polygons to multipolygons. However, where it makes sense to use multipolygons in NEW data, let us enter them as such. > I'd like to continue working on coastline, and map all remaining SMRs and > later maintain them. I also want keep using multipolygons in any regular > edits. Are there any objections? If by "regular edits" you mean adding NEW data, no, I have no objection. If you want to "convert" existing polygons to multipolygons, yes, I (and others) object. Thank you once again for good, productive dialog! SteveA California ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
On 20/11/2017 23:30, Ian Dees wrote: Please remember to stay on topic and friendly. This thread seems to be drifting off into a discussion about the merits of OSM editors. Well, my comment about editors wasn't supposed to be offtopic, since the question of data being "... far easier to understand and maintain, especially for novice mappers" was one of the points raised at the very top of the thread. It's perhaps worth mentioning that in each of iD, P2* and JOSM (without plugins) it's possible to swap without too much difficulty between the two relations and the constituent ways at http://www.openstreetmap.org/#map=19/36.62063/-121.90621 P2's internal visualiser fails with the park visualisation though, and I can't see a way to select the marine nature reserve without deliberately selecting the "relations this way is a member of" at the left, so I'm still not convinced that this area is as newbie-friendly as it was before. Best Regards, Andy * if you are surprised by this perhaps you haven't looked at one or another editor for a while - it might be worth revisiting. ___ Talk-us mailing list Talk-us@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-us
Re: [Talk-us] Multipolygonizing
On 2017.11.20. 23:29, Kevin Kenny wrote: > 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. revisiting this thread, i have to clarify that multipolygons for big objects like administrative areas, large national parks and similar entities seem fine to me, and often are the only reasonable approach. where they do not seem to provide benefit and only make things much harder are smaller objects - think most residential/commercial/industrial landuse, parking areas, buildings (except where used to "cut a hole" in a building). i got reminded about this when attempting to improve a fuel station recently. i intended to split car wash in a separate area, move tags from a node to area and similar. in this case, the serviceway area around the building, the building itself, the grassy areas there - they all were mapped as multipolygons from short way segments. i could have untangled that, but it would take some time. i gave up. > 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 a