I'd like to change the rendering of protected areas on osm-carto (the style which is used as a default map layer on the main OSM.org website). That proved to be a complex problem, however thanks to the comments from the community on the issue tracker and Talk list I see the general plan what to do. This entry is just a slightly edited message I sent to the list.
Exhibit A: Adirondack Park disaster...
TL;DR summary: I think that for now we should render all the existing tags, but make some of them appear earlier to encourage smooth migration to a more precise scheme.
As I currently understand it, nature reserve is always a type of protected area, to begin with.
We were talking on osm-carto ticket with some people about private reserves and even when someone told me "it's not about protection!" this term was used immediately in the same sentence (or in the next one). =} I guess they meant "it's voluntary and not formal", but still it's intended as a protection of nature, so it's just a special, weak type of protection.
The problem seems to be for a mapper to be more precise, since a typical survey can reveal a sign with a name "XYZ nature reserve". However this is not about just a name.
Boundaries are not visible on the ground easily, so a mapper who draw them has to use some other sources and I believe there are more informations available. Otherwise the area shape is probably not verifiable, which would be bad anyway. And I think all of them are areas, not the points (node would mean probably "here is the protection area, but exact shape is not shown at the moment"), so boundary is also a sure thing.
The name tag leisure=nature_reserve states that it's about leisure (which of course might be for a given object), but it's always about protection. So even if the value has merits, this key assumption is wrong in general and misses more important property (boundary=nature_reserve has only 35 uses).
Another problem is lack of coherent definition of protection (other than numbers) and lack of high-level classes.
The numbers seem to be derived from IUCN scheme, but wider: only categories 1-6 are IUCN-based and I don't know about the rest.
Especially class 7 is interesting for us: "nature-feature area: similar to 4. but without IUCN-level.", so i guess it's for all the non-IUCN classified nature reserves. Probably most of the time this should be clear from the boundary shape source.
It would be good to have more standardized subtags for common features:
- "nature" - protection_object=* is the same mess as numbers, when talking about hierarchy levels, so maybe some subtag like "nature_reserve=yes" would be useful
- "private" owner type (not the access type) - governance_type=private_landowner would be great (if really used...)
- "voluntary" - but that might be clear from the lack of government or international authorities influence
In summary, we have 3 popular but overlapping types now:
- leisure=nature_reserve (77 264)
- boundary=national_park (16 583)
- boundary=protected_area (62 016)
Their general properties and relations:
- has a wrong key, but nice value name, and is a subtype of 3.
- has a nice value name and a proper key, it's also subtype of 3.
- is very broad with precise, but not so common name, it also has subtypes, which are useful for official classification, but are not clear for all the other types of conservation
Therefore I would advice to:
Discourage leisure=nature_reserve and make it a subtag of boundary=protected_area (if needed, otherwise just use a protect_class=7 or other class if known), like:
- nature_reserve=yes - 2 uses
- protected_area=nature_reserve - 22 uses
- protected_area=nature - 61 uses
Drop boundary=national_park, since it's easy to identify them all and they are equivalent for boundary=protected_area + protect_class=2 anyway.
For rendering I would show all of them as currently, just using different zoom levels, starting from z8 currently (this might change in the future, of course):
- z8+: national parks and wilderness areas (both are big by definition)
- z9+: important natural protected areas (class 1-6, with hatched 1a probably)
- z10+: other natural protected areas (class 7, maybe also 12, 14 and 97-99)
- z11+: protected areas without class (if we know they're nature related) and leisure=nature_reserve
This is just a rough sketch, however it has some nice properties:
- all the existing schemes are visible (boundary=national_park can be dropped later)
- more important objects are rendered first
- less precise tagging is rendered later
Another important factor might be their size (so for example small national parks wouldn't be shown on z8) and a name (when the name is not tagged, push them later), but it needs a lot of worldwide testing.
(class 4 is the most popular)