[Tagging] Classifying roads from Trunk to Tertiary and Unclassified

[Paul Allen]

On Tue, 13 Aug 2019 at 04:23, Joseph Eisenberg <joseph.eisenberg at gmail.com>
wrote:

>
> Rather than using highway=trunk to define a autovia, motorroad or
> expressway with a certain maxspeed=, lanes=, or surface quality, I
> believe it is better to either 1) follow the national classification
> system, when this is logical and internally consistent,


Hard agree.  Even though it's starting to look like I live in the only
country
in the world with a national classification system that is logical and
internally consistent (and even we have a few rare exceptional cases). :)


> or 2) use network relationships and to assign a classification for a

 complete road route between towns. Changing the classification from trunk
>
 to primary to trunk again, in the middle of a rural area, breaks the
>
network.
>

I don't really agree on this.  It is possible for two trunks to be linked
by a primary.
In some cases it's mostly trunk from A to B with a bit of primary in the
middle.
In some cases two trunk routes, one from A to B and the other from C to D
have a primary linking them, and you'd use that primary to get from A to D.
And then there are cases where a section of a trunk road has been upgraded
to, or replaced by, a motorway.

UK map readers cope with these being rendered somewhat differently.
They're even
able to take secondary routes into account.  These things are coloured
whereas
minor through routes and non-through routes are not.  You look for the
coloured roads
linking A to B and try to figure out which is going to be best.

Where it goes wrong is people deciding that a trunk, primary, or even
secondary passing
through a town, city or village should be tagged as residential.

Certainly mappers should also tag maxspeed=, lanes=, surface=, and
> should map divided highways as 2 separate ways, and grade-separated
> intersections with bridge= and tunnel= + layer= so that routers will
> recognize faster routes.
>

Yep.  But I don't see those as a way of allowing one to tag primaries as
trunks.
They're a way of allowing routers to recognize that one particular primary
has
characteristics that are as good (or even better) than one particular trunk
where
either would be feasible alternative routes.

-- 
Paul
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