Validator: "water area inside water area" warning erroneous when natural=water inside natural=wetland

[liotier]

A water body inside a wetland is normal. Therefore, the JOSM validator must not warn "water area inside water area" when natural=water is inside natural=wetland.

[mdk]

If you map this way, the inner area has natural=water and natural=wetland at the same time. Mapnik renders smaller areas above larger, but it is not correct mapping, if the inner area is wetland AND water.

If you want that the inner part is only natural=water, you have to create a multipolygon with the natural=wetland as "outer" and natural=water as "inner" role.

[mdk]

Otherwise take a look at #9534.

[liotier]

If you map this way, the inner area has natural=water and natural=wetland at the same time

That is correct - or rather the way I see it: wetlands are complex objects - water bodies are part of them, cross them or partially overlap them.

[skyper]

Replying to mdk:

If you map this way, the inner area has natural=water and natural=wetland at the same time. Mapnik renders smaller areas above larger, but it is not correct mapping, if the inner area is wetland AND water.

What is correct? natural=water;wetland

[skyper]

In fact, we do not have a proper solution, yet. Mapping the wetland as MP with only the outer polygon is simply a cheat and reminds me about #19148.

[liotier]

I may be misunderstanding how to map that properly. Let me go to tagging@osm to confer - I'll come back with the consensus.

[mdk]

And as discussed in #9534 overlapping of natural=water and natural=wetland could be clarified!

[liotier]

The discussion at ​https://lists.openstreetmap.org/pipermail/tagging/2020-April/052280.html did not clarify whether overlap and full superposition have legit use-cases, but no one seems to disagree with multipolygons as the way to record any of such cases. So, the discussion will go on there, but this ticket car be closed. Thanks for your attention !

[skyper]

example file

[skyper]

Well, I will use multipolygons for all areas as there is no warning, but for me it is the same as all other examples.