I am not as experienced as all of you are on this subject and therefore my input will be limited. Surely though, I will take some time to study all these documents later this week - and even find out if there are any others that we might be missing. Regardless, I will try to point out a few things and hopefully this would be helpful to all of you - if not just ignore me…
Even if I am not familiar (as a driver) with every road in Greece, I am quite aware of the significance of provincial AND primary municipal roads (κύριες δημοτικές οδοί) especially in the region of Cyclades. The first ones are surely “the most important ones” in the region. The second ones are the “next most important ones”. There is a clearly distinction between those two and at the same time they are both more important than unclassified or residential ones. I really don’t think that BOTH of them could be mapped as “tertiary” or “secondary” roads, so there has to be another way to do that. Let me put it this way: Provincial roads are the main arteries of a local road network and as a result, they get most of the traffic and also most of the attention (as in funds for maintenance). Main municipal roads are also important enough, as they are almost always connected directly to the provincial roads and they do reach a village. They are not unclassified, and they surely aren’t as unimportant as residential ones.
In other words, I completely agree with this:
Here’s an actual example:
According to ΦΕΚ 47Α/1956, the island of Mykonos has two provincial roads:
1: Ormos Agiou Ioannou - Mykonos - Agios Stefanos
2: Mykonos - Ano Meria
There are of course many other roads which connect those provincial roads with other villages (and the airport in this case).
So, why main municipal roads are so important?
One answer could be found on ΦΕΚ 270Δ/1985.
More or less these roads are exactly what OSM wiki defines as tertiary ones. They are surely not as important as secondary ones, and they are surely not unimportant as residential ones. Of course some parts of these municipal roads might nowdays be irrelevant and have no actual use, but those could easily be “unclassified” (as the wiki suggest to do so, in case these roads are now quitter and unimportant).
But, which roads are the main municipal roads?
It’s easy to determine which are these roads just by definition (the same definition of tertiary roads, according to the wiki). Unfortunately, I can’t find a list and of course there are no signs. There are many random official documents (like this one) though, which both confirm their existence and their names.
TL;DR I do believe that a distinction has to be made between the lowest class of provincial roads and “un-gazetted” roads to villages.
Now, if these roads are highway=tertiary , then provincial roads should be highway=secondary or highway=primary, according to their actual classification. The documents which JayCBR provided are indeed helpful in most of the cases.
I’ve noticed though that ΦΕΚ 293Β/1995 doesn’t include the region of Cyclades. ΦΕΚ 423Β/1995 has an answer:
.
Therefore, to add something to Amaroussi’s scheme, highway=secondary could be used for these cases as well (I am sure he could find some words to describe it… e.g. secondary and unclassified provincial network? non-primary provincial network). Which by they way, I think it is exactly what most of us did, even before we had this discussion.