To make this a bit more concrete, here are the category definitions for a network:type (or if you prefer, route:scope tag), I would find useful and that might work globally:
- base_network : a local route, waymarked or otherwise explicitly signed specifically to create a network of accessibility for a non-car mode of transport (foot, bike, horse, …). Purpose is not necessarily touristic. This is essentially equivalent to the road network we describe with the main highway tags. Routes are usually not named and a single route usually isn’t considered a useful trip when followed from start to end.
- node_network: same as base_network except that each route starts and ends at an intersection clearly named or numbered.
- local: touristic route accessing one or more local features. Designed so it can be followed start to end. Day trip or less.
- regional: touristic route connecting multiple prominent features in a touristic region. Designed so it can be followed start to end. Should be a multi-day trip.
- interregional: touristic route crossing or connecting multiple touristic regions or crossing entire countries. Designed so it can be followed start to end. Full trip is 3 or more days.
- long-distance: touristic route covering large parts of a continent, usually crossing multiple countries (exceptions are North America, Australia and maybe Russia). Designed so it can be followed start to end. Full trip is at least a week.
Some additional observations:
Whether or not a route is designed to be followed from start to end or if it constitutes a base network is a bit of a subjective decision because many of the base networks for hiking have historically developed out of a collection of local touristic routes. I’d defer to local knowledge there. In Europe a good marker is if the route has an explicit name, not just a ref or a symbol. The US trail system can also be both. I’ve seen some trails that are clearly meant to be followed as a single trip. And I’ve seen trails that made up an entire network to give access to a hiking region so that you would switch from one to another on your trip.
Saying that the base_network is the same as the highway classification somewhat raises the question if it wouldn’t need indeed similar subcategories as primary/secondary/tertiary. So it might be orthogonal with [inrl]wn after all.
In areas where a good base network exists, the local/regional/interregional/global routes usually just follow routes from the base network. The result is that you usually follow the waymarking of the base network and find the symbols and names of the routes only on major guideposts (see also this thread). Ideally, we’d map that by making these routes superroutes containing only references to relations from the local network but practically this is not going to happen because data users can’t process that.
The definitions explicitly use “touristic region” instead of administrative region as these are often the unit of planning. In countries with a more centralized approach to planning (like Switzerland, Czech Republic, Netherlands and partially the US), administrative region might be a better fit.
In Europe, we also have the pilgrims routes, which are a bit of an odd-one-out. It’s not really a route but a network with many starts and one end. Can possibly be covered with a global scope and a special network=Camino de Santiago tag. Or might go into its own scope category.