Long in the past, some farangs started mapping in Thailand. Without a local community and without proper knowledge of Thai language, they set up some rules. Of course, they got some things wrong.
So what? It is possible to learn from experience, and to adjust rules to fresh knowledge. At least theoretically possible.
The original focus of OpenStreetMap is roads. Hence, the road network needs to mapped and structured, and some classification schema is required. Mappers decided to count the digits of the reference number, as this seemed to be a good fit for the roads they knew back then.
Relatively early, some mappers found out that some road reference numbers contain a prefix indicating the province (changwat) that was previously ignored (and is still ignored very often). They decided to categorize them at the same level as 4-digit-roads without prefix, so they could continue with the number counting classification.
And still nowadays, roads which do not have a reference number at all are not differentiated from roads which do have a number which just has not yet been mapped (and those are many).
Originally, there was a strict assignment from number of digits to the highway tag. In the current version of the wiki, one might assume that there is now some flexibility to one level upward or downward. But it is strictly not more than that, and even that one level is an extreme exception, as we see from several discussions.
But in fact, that system is fundamentally wrong.
Other countries managed to do things better.
Examples from France
Near Haguenau, road D 263 changes from secondary (south of town) to primary (in town, and north of town): https://www.openstreetmap.org/#map=15/48.7963/7.7687
Nearby, you can find tertiary roads with „D“ numbers (as for “Departement”, meaning “province”), like D 139. Near Strassbourg, there are roads with “M” numbers, also at secondary or primary levels.
The French wiki page https://wiki.openstreetmap.org/wiki/FR:Voirie just describes the meaning of the different highway levels, without using the administrative numbering.
Examples from Germany
While the administrative numbering schema generally fits well to the OSM highway levels, there are exceptions.
Road B19 is a primary north of the junction with motorway A7, and trunk south of it: https://www.openstreetmap.org/#map=14/49.8443/10.0097
But my favorite example is the South of Karlsruhe. Road K9657 is a “Kreisstraße” (county road, and county is one administrative level below “changwat”), so that would typically be a tertiary. But it is a trunk: https://www.openstreetmap.org/#map=16/48.9927/8.4237
South east of it, there is K9652 also at trunk level, and north east of it, K9652 at primary level, and a little farther to south east, K9652 at tertiary level.
Consequently, the German wiki page https://wiki.openstreetmap.org/wiki/Attributierung_von_Stra%C3%9Fen_in_Deutschland always admonishes that the administrative number is merely a „Richtschnur “ (“guideline”) and the actual “Verkehrsbedeutung” (“traffic importance”) is the actual criterion.
Oddly, while Germany has several “secondary” roads which do even lack a central line (not wide enough), Thailand has dual-carriage tertiary roads…
At OpenStreetMap, we prefer measurable criteria, which can be reproduced by other mappers, over “subjective” criteria where different people may reach different conclusions. A reference number is hence “objective”: you can go the signboard, and read it, and others will be able to read it in the same way (if they know the Thai alphabet, in some cases). But “traffic importance”? How can we measure that?
While one might argue that it works in Germany because of the generally high coincidence with the administrative numbering, the example of France proves that it does also work when the administrative numbers do not reflect traffic importance.
Edit wars do not seem to be common there.
In contrast, a small group of loud mappers in Thailand, aggressively discourages other mappers who follow international rules. They get accused of “cavalier mapping” or “vandalism”, and will see their contributions reverted. E.g.
Several of them did give up.
RocketMan (https://www.openstreetmap.org/user/RocketMan ) was last active some 7 years ago; he even removed his forum posts when he left.
Autoisme (https://www.openstreetmap.org/user/Autoisme ) was just recently discouraged.
Natthawee Chutianusornchai (https://www.openstreetmap.org/user/Natthawee%20Chutianusornchai/ ) also.
Yot Chaiyana (https://www.openstreetmap.org/user/Yot%20Chaiyana ) also.
The atmosphere here has long been toxic for new users, and also for some long-term members. A small group of people manages to enforce their style which is different from the rest of the world.
And because others refrain from using this forum (which uses English language, which many Thai people do not know; and which uses a farang communication style which is not at all compatible with typical Thai conversation styles), this small group thinks they are the majority.
No. The majority is not here on this forum.