[OSM-talk] [BOT] [RFC]: water surfaces

[Frank Villaro-Dixon]

On 16-03-22 16:46:03, Christoph Hormann, wrote 1.5K characters saying:
>On Tuesday 22 March 2016, Frank Villaro-Dixon wrote:
>>
>> Can you give me an example ?
>
>I probably could (after all i am on record for saying waterbody mapping
>in OSM is a practical case of the infinite monkey theorem) but right
>now i don't have the time to look for a good real world example.
>
>In principle many cases where the way you'd remove a tag from has
>additional tags the meaning of those tags will change when you remove a
>tag. 
For example ? I'm only focusing on natural= and water=
>Also cases where the way in question forms the division between two water 
>areas you will usually run into trouble.
No, because they are part of a relation multipolygon.
>
>On a principal level removing an ambiguity will always mean you remove
>possible interpretations of the data and your bot simply cannot know if
>the interpretations it removes are actually incorrect and the remaining
>interpretation is the correct one.
No,
If you have a lake with multiple ways grouped with a multipoly as shown:
R [natural=water water=lake]
W [water=lake intermittent=yes]
W [intermittent=yes]
W [natural=water]

It will be transformed as:
R [natural=water water=lake]
W [intermittent=yes]
W [intermittent=yes]
W []

Where's the other possible interpretation here ?

>
>> This algorithm won't loose any information. It's merely deleting
>> duplicates, so where is the problem ?
>
>You are only looking at it from a formal side and based on a specific,
>subjective interpretation of tagging rules which is not appropriate.
>See also
>
>http://wiki.openstreetmap.org/wiki/Automated_Edits_code_of_conduct
>
>As others have said the best way to improve waterbody data in OSM is by
>actually doing mapping work and correcting errors based on local
>knowledge or imagery.  You can believe me when i say that factual
>errors and inaccuracies are much more common and harmful problems
>w.r.t. water area mapping than basic tagging inconsistencies.
Try exporting all waterbodies them; you'll see that in the actual state, 
it's a royal pain in the ass. It's a shame because the quality of OSM is 
good, but it's really hard to work with this data…
>

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