# Re: [Tagging] [Talk-us] Trunk VS primary,

```On Fri, 20 Dec 2019 at 22:05, Graeme Fitzpatrick <graemefi...@gmail.com>
wrote:```
```
>
> But would they still count as either =trunk or =primary?
>
> While they're of high local importance, they're definitely not
> high-performance & they don't link major population centres either?
>

You have just identified three orthogonal dimensions:

- Construction (what you call "performance": motorway or dirt track)
- Traffic (number of vehicles per hour)

Depending on the country (or area of a country) those three may be highly
correlated or loosely correlated.  And even within a given area of a given
country, the degree of correlation may vary.

I put "importance" in quotes because I think it's really routeing.  If the
only
way of getting from A to B is along a particular road, it's very
important.  If
you can get from A to B via many routes, but one is by far the shortest,
it's
probably important.  OTOH if, of the many routes from A to B, one is very
much shorter than the others but one of the others takes far less time to
traverse then that second one is probably more important.  So I think
"importance" really means "routeing" (feel free to contradict me).

So how do we represent these three dimensions on a map?  I'd say we go
primarily by construction (with some concession to legalities, because
motorways/
freeways/autobahns have legal constraints that differ from other highways).
Traffic
rates are irrelevant to what is physically there (but have some bearing on
choosing a
route) and routeing is a decision left to algorithms.

Note that routeing algorithms can be run by a computer or they can be run
by wetware in a human brain looking at representations on a map.  So...

Is the route between A and B a motorway or a dirt track?  This is important
for
routeing algorithms on computers and in human wetware because it indicates
typical speed limits, legal requirements, etc.  Is this the shortest route
between
A and B?  A routeing algorithm can determine that whether it's represented
as
a motorway or a dirt track, and so can a human looking at a map.  Is it the
fastest route between A and B?  A routeing algorithm can determine that from
speed limits, but wetware is aided by seeing if the map renders it as a
motorway
or a dirt track.  Is it important?  Depends whether you want to go from A
to B or not,
but the desirability of using it to get from A to B is down to routeing
algorithms
(whether computer or human wetware).

So I come down firmly on construction (as modified by legislation0.  That's
verifiable.
All else is essentially routeing, whether done by computer or done by
wetware in a
human brain looking at a map.  Want to get from A to B?  That's what the
query tool
in standard carto is for.  Maybe one day it will offer the choice of
"fastest" and
"shortest" (maybe it already does).  Or just look at the map, as we boomers
are
used to from looking at printed maps, and figure out what the best route
might be.

Do we need to broaden our classes of construction/legality somewhat to
encompass
standards in countries outside the UK?  Probably.  Are the values for the
highway key
UK-centric and somewhat misleading?  Sure.  Should we map dirt tracks
between
Hell's Bumhole and Arse-end Of Nowhere as motorways because they're the only
way of getting from one place to the other?  No, no, a thousand times no.

--
Paul
```
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