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Mapnik doesn't render specific multipolygon configuration #3605

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openstreetmap-trac opened this issue Jul 23, 2021 · 2 comments
Open

Mapnik doesn't render specific multipolygon configuration #3605

openstreetmap-trac opened this issue Jul 23, 2021 · 2 comments

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@openstreetmap-trac
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Reporter: amdmi3[at]amdmi3.ru
[Submitted to the original trac issue database at 4.04pm, Thursday, 24th March 2011]

Situation:
Small fenced park (leisure=park+barrier=fence+name=) being an "inner" of a multipolygon representing a larger park (leisure=park).

The problem: smaller park is not rendered by mapnik (even the fence is not rendered). If I change leisure=park to e.g. landuse=grass, both polygon and fence are rendered, however such tagging is not really correct.

I believe that's part of "compatibility" with broken multipolygons which are expected to have tags which belonging to multipolygon on both inner and outer ways. In any case, it should be fixed, as it prevents rendering properly tagged objects correctly, while masking data errors (however, I haven't seen such broken multipolygons in a first place).

Here's the problem:
http://osm.org/go/0t21K6eJK--

@openstreetmap-trac
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Author: Ldp
[Added to the original trac issue at 6.27pm, Friday, 25th March 2011]

That seems to be correct. Multipolygons where both outer and inner ring(s) have the same tags are understood to be one and the same, and no geometry is created for the inner part.

This is due to early multipolygon understanding by many mappers. Perhaps it's time to eventually rethink this assumption and just deal with the fallout (early multipolygons).

@openstreetmap-trac
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Author: AMDmi3
[Added to the original trac issue at 11.34pm, Monday, 7th April 2014]

Note that the link in the defect description no longer demonstrates the problem - I've worked it around by creating multipolygon out of inner ring as well. But still it's really time to drop legacy and avoid the need for such workarounds - I haven't seen legacy multipolygons (with tags on outer way instead of relation) for a long time already.

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