I can not see any difference and in my understanding a route marker is not a real guidepost, that’s why it has it’s own value for the information-tag, beside information=guidepost. And if that is the case, guide_type=intermediary is unnecessary and should be discouraged in the Wiki.
Some of the guide_type=intermediary-nodes actually have a name-tag (Overpass-Query).
However, it seems to me that most of these “names” should not even be in the name-tag. Especially the 159 instances of name=GR13 Wrong way (Overpass-Query)
I agree that guide_type=intermediary should be deprecated (with information that one should use information=route_marker provided) as it is not a guidepost. It might get its ~1k uses because until about a year ago the wiki did not have that information=route_marker mentioned as the alternative at that place in the table (which it now does, but without explanation that it is better and more popular tag to use).
The most obvious difference is that a guidepost is an actual post or similar infrastructure. A route marker is just stuck on something else (similar to trail_blaze). guide_type=intermediary says that the guidepost isn’t providing more information than a route marker, but it is a guidepost, not just a sticker attached to something else.
The small plate further down is a route marker on this relation. Had it just been stuck to a tree or fence post or similar I’d map it as information=route_marker, but here it’s actually attached to a guidepost, so it makes sense to add the same node for that guidepost to the other relation too.
But isn’t that what we use support=pole / support=tree / etc. for? My understanding is that a guidepost shows detailed information what can be found where (“[…] indicate the directions to different destinations”) and a route marker just tells you “yep, you’re still on the right track, keep going” or “keep right”, without telling you for which purpose exactly (“[…]shows the position of the way of a route”). Both can be on a pole or a tree or wherever else
Only 15 instances of information=guidepost + guide_type=intermediary in all of UK isn’t exactly much either.
…and Italy. Over 14000 guideposts worldwide with a support-tag is actually not just “a bit”. Agreed, almost all of them are in Europe, but same goes for guide_type=intermediary. Only 7 (!) instances of the latter are not in Europe.
A guidepost on a pole is a guidepost, a guidepost on a tree is a guidepost, a routemarker on a tree is a routemarker, but a routemarker on a pole is an intermediary guidepost…?
That doesn’t really make sense. The only difference is the location/support of the routemarker, and the location/support should not be important enough to change the value of the information-tag itself to something completely different.