[OSM-talk] Rendering issues with Carto 4.0

[Christoph Hormann]

On Tuesday 20 June 2017, Jochen Topf wrote:
>
> Unfortunately nobody really realized that as a side-effect of the
> update to Carto 4.0 many multipolygon relations would appear wrong on
> the map. This is the case for multipolygon relations that have the
> same tags on the relation as well as on (some of the) outer or inner
> ways. This is *wrong* tagging, and needs to be fixed. Note that this
> always was wrong tagging, even before we deprecated old-style
> multipolygons, but the way the software worked with old-style
> multipolygons, this problem was not visible on the map.

You are completely right with the analysis of the problem but we did 
realize this before releasing osm-carto 4.0:

https://github.com/gravitystorm/openstreetmap-carto/pull/2533#issuecomment-300167850

The problem is simply there is no good alternative to going cold turkey 
here - any compromise solution would have meant to perpetualize the 
problems due to the 'over-cleverness' in tag interpretation of old 
style multipolygons.  It should be clear to everybody that now that old 
style MPs are gone in the data tag interpretation on ways will become 
completely independent of if they are member of a relation or not - 
which is a good thing and ultimately should also make it easier for 
mappers understanding how multipolygons work.

-- 
Christoph Hormann
http://www.imagico.de/