[Tagging] Multipolygon (several outers) forest with different leaf_types: mapping strategy?

[Andy Townsend]

On 13/03/2019 13:59, David Marchal wrote:
> I mapped a forest made of several pieces of woodland, some contiguous 
> and some isolated, with differents leaf_types. I mapped this 
> (https://www.openstreetmap.org/relation/9393253) with a landuse=forest 
> multipolygon, with common tags such as name and operator on the 
> relation, and with leaf_type tags on the outer members, as each has a 
> different value. It seemed a good way to model the fact that these 
> woodlands were considered part of the same forest but had differents 
> leaf_types, but I am unsure now: the JOSM validator claims that 
> contiguous outer members is an error, and openstreetmap.org renders a 
> misplaced name and no leaf_type. Is it a modelling failure or a 
> renderer and validator error? In the first case, how should I map this?

Using a multipolygon relation like this makes sense when the objects are 
exactly the same, but not when they aren't, so that probably explains 
the validator issue.


Name placement on multipolygons like this is actaully a renderer 
decision - some will use one name per group of trees, some one name 
placed somewhere near the biggest.


I'd probably map your trees as either:


1) natural=wood; name=whatever; operator=whatever; leaf_type=whatever on 
each group of trees.  This will result in duplicated names, but isn't 
that different to the way we split roads when other tags change.


or


2) natural=wood; leaf_type=whatever on each group of trees, and create a 
landuse=forest multipolygon relation with name=whatever; 
operator=whatever that includes each group of trees.


or


3) If the "managed forest area" by operator=whatever includes 
significant area of no trees currently, natural=wood; leaf_type=whatever 
on each group of trees, and create a landuse=forestry multipolygon 
relation with name=whatever; operator=whatever that includes each group 
of trees or no trees managed by the same organisation.


The whole landuse=forest/natural=wood thing is fairly contentious 
though, so please don't take the above as "what everyone does in OSM"; 
it's just how I'd map it.


Best Regards,


Andy


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