[OSM-talk] Waterway rel with mix of line & poly

[SandorS]

Jem,
you have, of course, fixed the issue already. That was the right ting to do. Though, there are many, many similar cases and not only in natural=water tagged geometries. Many users run a geometry-model based recognition program that detects and repairs these problems even not knowing they were there. 
However, two comments from the last mail deserve some further comments.
>>	Relations should not be used to collect thing together.
>>? That is what they can be used for. See the site relation as an example.
Yes, “they can be used for” but here OSM wiki is explicit “should not be used” (obligatory restriction). Besides, when I see/search the OSM wiki using the “site relation” key I got this https://wiki.openstreetmap.org/wiki/Relations/Proposed/Site. It is a proposal just like many other “collecting thing together” proposals like multiobject, group, cluster... Using these proposals in private database versions is up to the users but should not be used in OSM data source. Otherwise, mappers can cause damage to others, serious professional mismatch and huge data and work redundancy. Just look at this https://osm.org/go/cAO2c--?relation=1124369. Why, just for the Wikipedia link or some never used names?
>>	MP relations should be restricted to the areas which have inners:...
>> No. They can be used to collect a series of outer ways to form the boundary of a feature e.g. an administration boundary usually shares ways with adjacent
>>administrations
Irrelevant contrast.  However, the second line perfectly illustrates how to present an administrative (political) AREA feature using MP. Because of many rendering issues related to overlapping areas, if only the area boundary is needed, OSM wiki has introduced the “boundary” as a new tagging key and using MP declared deprecated for that purpose. The suggestion in the first line is not acceptable for now. Simply, we don’t have other tools to represent areas with just one border line when the number of border nodes (considerably) exceeds the node number limit in the “way”.
Sandor

Sent from Mail for Windows 10

From: Warin
Sent: 21 September 2018 01:33
To: talk at openstreetmap.org
Subject: Re: [OSM-talk] Waterway rel with mix of line & poly

On 21/09/18 06:11, Jem wrote:
Thank you both. That's very helpful.

On Thu, 20 Sep 2018 at 22:25, Dave F <davefoxfac63 at btinternet.com> wrote:
Hi

Short answer: Yes

There's a few problems here:

Relations should not be used to collect thing together.
? That is what they can be used for. See the site relation as an example. 

There shouldn't be tags on the ways which conflict with those in the relations
True.

MP relations require a 'type' tags and 'inners' & 'outers' roles
True

In this case the Southern section shouldn't be a polygon 
Did not look.

MP relations should be restricted to the areas which have inners: https://www.openstreetmap.org/relation/2571440#map=19/51.15275/-2.05045
No. They can be used to collect a series of outer ways to form the boundary of a feature e.g. an administration boundary usually shares ways with adjacent administrations. 

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