[Tagging] Why is this user editing in this manner?

Frederik Ramm frederik at remote.org
Thu Aug 16 07:58:23 BST 2012


On 08/16/12 06:16, Jais Pedersen wrote:
> Looking at his other recent edits, it looks like he is systematically
> going through and fixing the issues in OSM Inspectors Multipolygon view:
> http://goo.gl/aWpXQ - It still shows the error as i write this, but the
> view might have been updated with his edits by the time you click the link.

The tagging that Dave described - a closed ring adjacent to a 
multipolygon, and sharing a few nodes with the multipolygon's outer ring 
- is not an error. OSMI checks things object by object and therefore 
would not even be able to detect a problem that arises from two totally 
seperate objects (e.g. it would not be able to detect two buildings 

My personal take on the tagging style is that I'm happy to use Dave's 
style if the number of nodes shared by both objects is less than 10, but 
if it becomes more I'd choose the kind of tagging that the other guy 
used. But neither is wrong and this is a matter of personal taste.

What is *not* a matter of personal taste, and what OSMI usually 
complains about, is when the polygon geometry cannot be built due to

* unclosed rings (dangling segments)
* self-intersections within one ring
* overlaps between different rings

The Inspector is sometimes less than clear about what its problem is, 
exactly, and you often have to take a closer look. The Inspector is 
nearly always right in detecting "something fishy" but it is not always 
immediately clear *what* the fishy thing is. In this specific case, I 
believe the error persists in the current version of the relation:

   <relation id="1754193" visible="true" 
timestamp="2012-08-15T18:44:57Z" user="mentor" uid="38588" version="14" 
     <member type="way" ref="173633663" role="outer"/>
     <member type="way" ref="125820705" role="outer"/>
     <member type="way" ref="125820705" role="outer"/>
     <member type="way" ref="140782843" role="inner"/>
     <member type="way" ref="140782844" role="inner"/>
     <member type="way" ref="140783771" role="outer"/>
     <member type="way" ref="175005862" role="outer"/>
     <member type="way" ref="130171853" role="inner"/>
     <member type="way" ref="173633664" role="outer"/>
     <member type="way" ref="130171898" role="inner"/>
     <tag k="description" v="River Avon"/>
     <tag k="source" v="Bing"/>
     <tag k="type" v="multipolygon"/>
     <tag k="waterway" v="riverbank"/>

Way 125820705 is there twice, making it impossible to build a proper 
outer ring out of all the "outer" ways.


Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"

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