[karlchick]

I came across a „filled in“ lake in Wales, see second attachment image.
I went back to an older map version from 2021 and the lake looked normal, see first attachment image.
Looking at the OSM data I found that someone has tried to add an outer rim of intermittent water to the existing lake, and they used the existing lake as the inner polygon (see 3rd image).
Logically this makes sense, the inner „hole“ would be the lake, so you would expect the lake to also be rendered…
however the OAM map data seems to be missing the lake and have just the outer „rim“ of intermittent water.

Question is: Is this an issue with the OSM map data (the way it is defined)? or with the generation of the OAM map?

[ChristianK]

Hi Karl,

Mapsforge has its limitations when it comes to resolving such artworks.
This affects all maps based on Mapsforge, not only the OAM.
Unfortunately mapnik, the standard renderer for OAM, is much too forgiving and renders even real worse mappings.

I’ll take a look at it.

Happy new Year
Christian

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karlchick

[karlchick]

Hi Christian,

Here is the url to the osm item that I think causes the issue:

https://www.openstreetmap.org/relation/13240062#map=16/51.8819/-3.7421

Adding a ring if intermittent water to a lake seems a bit pointless I this case, as there are no footpaths affected by it… but if such a feature was required, I’m wondering what the correct way to map would be… perhaps duplicating the lake and using the duplicate as an inner?

[ChristianK]

Hmm..

Not too complicated, no intersections, it _should_ render….
However, this is the first occurence of a Relation where lake/water is within water I see.
Interesting but unecccesary like wet socks – sorry..

The maker of Renderlibrarys like Mapsforge can’t thing of every possible kind of mapping-artwork 🙂

Solution: unfortunately none without starting a mapper-war.
For me this relation have to be deleted cause every lake has its faling and rising water-level, its crazy to convert all lakes in Relations with intermidient water.

[ChristianK]

So..

The tagging is perfect correct !!
See: https://wiki.openstreetmap.org/wiki/Relation:multipolygon#One_outer_and_one_inner_ring

When I replace the tag for the relation = outer ring from natural=water to natural=forest the lake renders fine.
Changing back to natural=water the INNER does’nt render.

Strange!

Well, this seems to be a glitch in the Library – unfortunately I can’t do anything in this case…

Maybe @EMUX can take a look at this issue ?

[Autor]

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