Changeset: 136645299
Deduplicate some more areas
Closed by tms13
Tags
created_by | Merkaartor 0.19.0 (en) |
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Discussion
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Comment from watmildon
Hello!
Can you help me understand why some of the features have been grouped into multi-polygon relations when I would expect the already existing tagged ways are preferable? For example this: https://www.openstreetmap.org/relation/15912391
In general, my experience is that grouping things like this just makes edits more cumbersome for other mappers and I don't see how these areas of scrub are logically "one feature".
There's also this relation that previously was a simple way https://www.openstreetmap.org/way/968226915 ... the benefit is unclear.
Any clarity you can provide is appreciated.
Thanks!
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Comment from tms13
The duplicated edges tend to fall out of sync when edited so that abutting areas end up overlapping or not quite meeting. This particular area was highlighted by OSM Inspector due to touching rings, so I fixed up some of its duplicated boundaries whilest editing.
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Comment from tms13
It's a judgement call whether the scrub is a single feature or not - feel free to separate into smaller relations if necessary.
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Comment from watmildon
Thanks for the reply. My general feeling is that having multi-polygons with only outer members (https://www.openstreetmap.org/relation/15912390) (https://www.openstreetmap.org/relation/13951181) achieves very little and makes it more difficult for other editors. Entangling too much geometry into relations creates a burden down the line in my experience.
In the interest of having a more concrete discussion, I've submitted my preferred way to map things like this and would appreciate it if you could take a look and let me know if you think any nuance is lost. If I've damaged things then I can revert and will have learned something interesting.
https://www.openstreetmap.org/changeset/136948759
Thanks!
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Comment from Woazboat
> The duplicated edges tend to fall out of sync when edited so that abutting areas end up overlapping or not quite meeting.
I assume by 'get out of sync' you mean that the two closed way areas that used to perfectly share an edge are no longer identical along that edge and there are either holes or overlaps where one of the ways has some extra nodes/is missing some nodes somewhere in between?
I'm not quite sure I follow that argument. Deleting or moving a node always affect all parent ways and cannot make them go out of sync. When adding a new node into a way, pretty much all editors simultaneously add them to all overlapping ways that share the same way segment so that they are still in sync and attached (and if they don't, they shouldn't be anywhere near users who don't know exactly what they are doing). Detaching the ways from each other is actually harder than keeping them overlapping and really has to be done intentionally.
The one way that overlapping or not quite seamless areas can happen is if they are created that way and were never attached in the first place. Often there is a reason why there's a gap in between and if there isn't, they can simply be attached by merging the nodes to make them overlap. -
Comment from tms13
Yes, that's exactly what I mean about ways that start off identical and then diverge. I've not used an editor that adds to multiple ways simultaneously - I didn't know that there are some that can do that. I'm certainly seeing unintended overlaps and gaps between areas. And also linear features that clearly ought to be the delineation between areas (fences, walls, hedges, etc) getting out of sync with their respective areas. I always understood it to be best practice to use these boundary ways to form the areas.
Having multiple ways sharing the same nodes certainly makes it very difficult to select the way you actually want to edit much of the time. -
Comment from watmildon
For folks using iD and JOSM, having a bunch of relations in the editing area can make things quite frustrating to edit.
I totally hear you about selecting can be a bother. iD has '\' as a hotkey for "select the next way that shares this node" and JOSM has the rather cumbersome "middle click to cycle through coincident objects". It's also not helped by iD trying pretty hard to hide that relations are a thing or JOSM pulling all relation selection/editing into it's own side interface. And don't get me started on relations of relations ha.
I'll have to fire up Merkaartor sometime, differences in editors definitely can make "best practice" more difficult.
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Comment from Woazboat
> I always understood it to be best practice to use these boundary ways to form the areas.
It's certainly not how the overwhelming majority of editors do things. Simply because it doesn't really offer any benefits and only complicates things. Multipolygons should only really be used when they are necessary (e.g. when there's a hole in the area).
> For folks using iD and JOSM, having a bunch of relations in the editing area can make things quite frustrating to edit.
Normal editing operations such as changing tags or moving the outline around a bit work more or less fine and you won't even necessarily notice that you're editing a multipolygon. Even iD has that rudimentary level of support. Anything that involves creating new areas or deleting (parts) of areas is going to be more of a hassle than it needs to be though.
More problems start to pile up when you want to do things that are a bit more advanced, such as joining or splitting areas, etc... Editor support for operations on multipolygons simply is not as good as it is for simple closed ways. E.g. splitting multipolygon areas wasn't supported in josm and had to be done manually until I implemented it recently while it has been available for normal closed way areas for ages. These problems might not be as noticeable for users of editors that don't have these features in the first place and where doing things manually is the only way anyway, but it's a big annoyance and slowdown for users of advanced editors.> Having multiple ways sharing the same nodes certainly makes it very difficult to select the way you actually want to edit much of the time.
> JOSM has the rather cumbersome "middle click to cycle through coincident objects".
You can select areas as normal by double clicking in them (josm), so selecting different closed way areas even when the ways are partially overlapping is a non-issue and you won't even notice it. If there are multiple linear ways overlapping, you can select them by cycling through them by holding the alt modifier key while clicking or selecting them from the popup list that appears when middle clicking on them.
> JOSM pulling all relation selection/editing into it's own side interface. And don't get me started on relations of relations ha.
Editing multipolygons works just like for any other objects. You _can_ select and edit them using the relation editor if you want to, but that is rarely necessary. Using the dedicated relation editor interface for other relations is a good thing since the properties of relations are so different to other objects and the normal editing interface is not intended for that (e.g. you need to be able to edit the member objects somehow).
Relations of relations are not relevant for multipolygons or areas that are the topic here.Anyway. The multitude of issues with overlapping or not quite joining ways here in this area seem to have been here since they were created by a user who apparently didn't care too much and were not created by subsequent edits. This is not something that is an inherent fault of simple closed way areas.
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Comment from Woazboat
> It's certainly not how the overwhelming majority of editors do things.
By 'editors' I mean users/humans in this instance
Ways (1-20 of 25)
- 1
- 2
- 968226915, v6
- 1176851999, v1
- 968226909, v2
- 968226910, v2
- 968226911, v2
- 968226914, v3
- 1038100019, v8
- 1176852000, v1
- 1176852001, v1
- 1176852002, v1
- 1176852003, v1
- 1176852004, v1
- 1176852005, v1
- 1176852006, v1
- 1176852007, v1
- 1176852008, v1
- 967952772, v4
- 1176852009, v1
- 888464492, v3
- 888464499, v3
Relations (6)
Nodes (3)
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