[Tagging] Meaning of way/node/area/rel in the tag documentation template

[Tobias Knerr]

On 04.10.21 14:46, Martin Koppenhoefer wrote:
> I am wondering what the meaning of the object types for tags is. (on 
> node: yes, etc.)
> Is this about possible use? Actual use?

I consider it to be about what object types the tag _should_ be used on 
(either according to proposals/consensus or, failing that, according to 
what can be inferred about mappers' intention from existing use in the 
database).

If it was about actual use, it would be redundant with the Taginfo 
statistics in the same template.

> Do we really have tags where usage on certain element types is 
> "forbidden"?

There are plenty of tags which data consumers will (rightfully) not 
expect to be used on certain element types, and which other mappers will 
probably treat as an error as well.

For example, a highway=motorway tag on a node is very likely a tagging 
mistake, and won't be useful for many applications.

> How can we say that a tag cannot be used on a relation, if 
> there are infinite types of relations?

We can say this by only considering the finite number of currently 
established relation types.

Of course, it is possible that someone will invent a new type of 
relation where that tag will make sense to use. When that new relation 
type gains traction, the documentation can be changed from onRelation=no 
to onRelation=yes.