Thanks for bringing this up! Parks and protected areas is something I think about a lot in OSM.

I would oppose using protect_class for any sort of primary class logic. The numeric classes are poorly defined ("loosely based on IUCN categories") and for the stranger (and rarely-used numbers), completely made up. There are only a rare handful of exceptions for objects tagged boundary=protected_area where you wouldn't want to treat them as any other nature reserve for styling. I think that openstreetmap-carto makes a mistake in limiting protected area rendering to specific protect_class values.

The class value should ultimately be linked to some rationale for styling. The only categories I think that renderers really care about for styling differences are national parks, nature reserves (protected areas), indigenous lands, ordinary parks, and recreation grounds. I would favor something vastly simpler, like this:

class=national_park

• boundary=national_park

class=protected_area

• Any boundary=protected_area
• Any leisure=nature_reserve

class=aboriginal_lands

• Any boundary=aboriginal_lands

class=park

• Any leisure=park
• Any landuse=village_green

class=recreation

• Any landuse=recreation_ground

As part of this reshuffle, I would remove leisure=park, landuse=village_green, and landuse=recreation_ground from the landcover layer, because these features are properly parks, and not landcover.

I think protection_title is not really useful for rendering and can probably be dropped. If we wish to keep it, it makes the most sense as a text field rather than a lower-cased enumeration.

I noticed an issue with the classes of all the French national parks. They show up as "cœur" or "aire_d’adhésion" instead of "national_park".

Screenshot taken from: https://onthegomap.github.io/planetiler-demo/#6.1/45.297/4.945
Data is the same on: https://cloud.maptiler.com/tiles/v3-openmaptiles

OSM properties:

• Mercantour (between France and Italy): https://www.openstreetmap.org/relation/1024511
• Cévennes: https://www.openstreetmap.org/relation/1024512
• Calanques: https://www.openstreetmap.org/relation/3080199

I think that's related to this issue. Otherwise, I can open a new one.

So right now, these national parks can not be displayed in any map styles. Do you know how to fix this?

Is there interest in reducing the number of class values in the park layer to something sane? I'd be happy to take a crack at that.

It would be great to clean up park layer. Thanks!