Hello Marian,
[...many ideas...]
I'm thinking about a how to define a scheme that can cover all of this, but I want to go to bed now, so I'll do that tomorrow, but already send this mail to avoid people considering the discussion over ;)
As there are many different criteria, maybe a multicriteria scheme would be helpful?
For instance having 3 criteria like * tags specifying transport systems with regular stops or single stops at this station (e.g. railway:station:long_distance = no|single|regular, railway:station:local = no|single|regular and so on) * tag for category considering number of travellers and station equipment (similar to German "Bahnhofskategorie") * tag for dominance specially considering main stations / central stations and important interchanging nodes
Of course, this scheme does not solve linearization problem of station importance for rendering. But it corresponds to real-world data. I guess linearization/ordering of stations for rendering could be done by the renderer itself using map styles? Later on, a map style could be changed without changing the tagging.
Micha