[Tagging] Branched and alternative roujtes

Kevin Kenny kevin.b.kenny at gmail.com
Mon Aug 19 14:11:44 UTC 2019


(Summary: What do the data *consumers* want to see in the tagging for
route alternatives, circular routes, and routes that begin and end on
dual carriageways?)

On Mon, Aug 19, 2019 at 3:47 AM Sarah Hoffmann <lonvia at denofr.de> wrote:
> We do happen to have a clear rule for unbroken linear routes: just assemble
> in the obvious way, no matter if sorted or unsorted. We don't have any rule
> for anything more complicated that mappers can follow to get the desired
> effect. We already fail with something as simple as a directed unbroken
> linear routes and circular routes. There is no single recommended way to
> define the start point.

A circular route may not even have a start point.  Hikers doing the
Carnberry Lake 50 can start and end it anywhere and do it clockwise or
anti-clockwise (although there happen to be only a couple of good
places to get on and off the circular route).

> Assuming we don't care what happens to really botched relations, all cases
> except one that I listed initially are covered with one single simple
> instruction to the mapper: sort your route.
>
> What remains are routes which are split/have alternatives/access routes etc.
> Gut feeling tells that roles will solve those cases but I get back to you
> on that once I had a go at implementing it.

If I recall correctly, you're well on the way to handling role=forward
and role=backward splits - I seem to recall that WMT was fairly
graceful about the one or two of those I put in (to repair routes that
were broken altogether - I'm not in the habit of editing cycling
routes otherwise).

For hiking routes, the splits that I have and don't quite know how to
manage are:

- Short diversions. Some of the trails that I've mapped have short
segments for winter and summer routes, or marked alternatives for use
in case of high water, fire-season trail closures, or beaver activitty
(which, I suppose is a special case of high water).

- Access ways. Ordinarily these are marked separately from the main
trail and I just carry them as separate routes. The only case where
I've really wanted to make some sort of association is that the Green
Mountain Club, in addition to the 'end to end' award on the Long Trail
(for hiking the main stem) offers a much more difficult 'side to side'
award for hiking each of the approach trails. I have Absolutely No
Idea how to represent this, if I were to do so.

- Major diversions. For the 'end to end' award on New York's Long
Path, the suburban sections in Orange County are recognized to be a
problem for hikers, and a recognized alternative is to leave the Long
Path in Harriman Park, follow the Appalachian Trail to High Point, New
Jersey, and then the Shawangunk Ridge Trail to rejoin the Long Path in
Otisville.  I'm perfectly fine, though, with simply offering this as
narrative, and having the relations show this as three separate
trails. Hikers have to make their own decisions sometime!

- Trails that are waymarked only in one direction. I do this with
'oneway=yes' on the relation, and order the ways accordingly, but I
did encounter a circular route that seemed to be ambiguous however I
did it. (The trail maintainers rendered this one moot by installing
signs facing the other way.)

The same sort of things seem to infect road routes:

- Routes that begin and end at the interchanges among dual
carriageways, which give no single point that can be indentified as an
endpoint because the geographic endpoints are different in the two
directions. JOSM has a real problem sorting these.

- Multiple-carriageway routes, where there are grade-separated ways
between 'express' and 'local', or between 'auto' and 'hgv' or between
'vehicles with transponders' and 'vehicles paying cash'.  This is an
additional layer of split on top of 'forward' and 'backward' and is
even worse for messing up sorting.

- The same thing can happen on surface streets where there are
numbered routes that are bannered 'ALT, 'BUSINESS', 'TRUCK', etc. For
these, though, I'm perfectly fine with saying that the loops and spurs
are entirely separate routes. The signage is distinct, and people in
the affected areas are used to being directed onto 'US 20 Business' or
whatever.

We have 'forward' and 'backward' pretty much conquered (except for the
dual-carriageway case). WMT already appears to figure it out, (well,
mostly), and JOSM successfully sorts these, even when routes traverse
roundabouts.

I'd like to hear from data consumers in particular what tagging they'd
like to see for

- diversions and alternatives
- routes with different endpoints in the forward/backward directions
- spur routes
- one-way routes that may be circular

[End of technical discussion. Political jeremiad follows. Feel free to ignore.]

With my data consumer hat on, I want to be able to consume the data
describing these situations without having to guess, because computers
are very, very bad at guesswork.

With my mapper hat on (the current one is a faded and stained baseball
cap bearing the logo of a trail crew), I want to produce data that
will be useful to consumers. I am told that there are other mappers
who are more 'artists' interested in describing the world around them
without regard to utility, but I think that most mappers would agree
with me in wanting the data to be useful to others.

That's why I'm interested in hearing specificallly from data consumers
- just as mappers have the actual knowledge of what's in the world,
consumers have the actual knowledge of how to aggregate it and present
it to others in a useful fashion.

I'm willing to conform with reasonable mapping guidelines. Where I've
objected in the past to specific mapping guidelines, it's because of
one of these sorts of things occurred:
 - the guideline amounted to 'don't map that!'
 - the guideline was self-contradictory
 - the guideline provided me no way to distinguish features that my
rendering needed to distinguish. (That is NOT 'tagging for the
renderer,' guys!)
 - the guideline provided me no way to 'rough out' features that I'd
observed in the field without needing to return for more observations.
(Or worse, provided no way to map the object without doing research at
home because information needed for conformance was not observable in
the field.)

For many 'it's too much work for the mapper' objections, the solution
is 'make the editor smarter', and the maintainers of the editors have
been quite good about responding to tagging schemata that actually
solve a problem and come into common use.

-- 
73 de ke9tv/2, Kevin



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