[Talk-us] Rewriting route direction documentation to emphasize subrelations

[Minh Nguyen]

I added a table of statistics to 
<https://wiki.openstreetmap.org/wiki/Route_directions#Statistics> with 
links to Overpass queries that you can customize for the route network 
(or cycle_network) you’re interested in.

As of today, about three quarters of Interstate way mileage is covered 
by either method of tagging cardinal directions. Directional roles in 
bidirectional route relations cover 40% more distance than 
unidirectional route relations, but only 63% of the overall distance of 
bidirectional route relations.

About a quarter of U.S. Route way mileage is covered by either method. 
Directional roles cover more than twice the distance of unidirectional 
route relations, but only 20% of the overall distance of bidirectional 
route relations. It’s a huge gap that probably hasn’t changed all that 
much since 2013.

California has always used unidirectional route relations pretty 
consistently for divided highways, but routes along surface streets are 
largely untagged with directions, as in many states.

Vào lúc 12:46 2021-07-31, Tod Fitch đã viết:
> I don’t have a good feeling about how the whole country is, but all 
> the freeways I have looked at in California have three relations (1 
> master and one each for the cardinal direction). In my area the US 
> routes are mostly but not all using three relation scheme as are a few 
> California state routes. At least for my editing style using JOSM, I 
> much prefer the super/sub relation scheme as I find it easier to fix 
> things when broken.
>
> —Tod
>
>> On Jul 31, 2021, at 6:19 AM, Clifford Snow <clifford at snowandsnow.us> 
>> wrote:
>>
>> Do you know what portion of the Interstate system has been mapped 
>> with route directions? What about US routes?
>>
>> Clifford
>>
>> On Fri, Jul 30, 2021 at 11:37 PM Minh Nguyen 
>> <minh at nguyen.cincinnati.oh.us> wrote:
>>
>>     The article has been rewritten according to the draft and renamed to
>>     reflect signage and tagging practices in Canada and New Zealand
>>     as well:
>>
>>     https://wiki.openstreetmap.org/wiki/Route_directions
>>
>>     Vào lúc 17:55 2021-07-24, Minh Nguyen đã viết:
>>     > Back in 2013, a discussion on this list [1] led to a wiki article
>>     > documenting how to indicate the cardinal direction along a
>>     route, such
>>     > as the "north" in northbound I-75. [2] I've drafted a rewrite
>>     of this
>>     > article at [3] and would like to get the community's feedback
>>     on it
>>     > before touching the original, which has often come up in
>>     discussion. The
>>     > rewrite attempts to clearly explain route directions for both
>>     domestic
>>     > and international audiences. These days, overseas mappers are very
>>     > active in navigation mapping, and route directions are also
>>     relevant to
>>     > some non-English-speaking regions.
>>     >
>>     > According to the original documentation, setting relation roles to
>>     > cardinal directions is preferred over creating a separate
>>     relation for
>>     > each direction and setting direction=* to the cardinal
>>     direction (and
>>     > joining the relations in a superrelation). The rewrite reverses
>>     this
>>     > guidance, placing more emphasis on subrelations and
>>     superrelations than
>>     > relation roles.
>>     >
>>     > The directional roles have had the advantage of being easier to
>>     > introduce than superrelations, especially for routes that only
>>     > occasionally run along divided highways. That was important
>>     early on,
>>     > when route relations were first being built out. However, it
>>     has tended
>>     > to result in routes that are only partly tagged with cardinal
>>     > directions, requiring data consumers to infer the cardinal
>>     direction
>>     > along ways with forward, backward, or unset roles.
>>     Additionally, editors
>>     > and quality assurance tools have not added specialized support
>>     for these
>>     > roles as they have for forward/backward, so existing coverage
>>     has been
>>     > fragile.
>>     >
>>     > Although subrelations and superrelations are initially more
>>     difficult to
>>     > create, they are easier to maintain in the long run and are
>>     already
>>     > well-established for major road routes as well as public
>>     transportation
>>     > routes. I see them as part of a natural progression in OSM towards
>>     > greater detail, coverage, and structure.
>>     >
>>     > This would only be a rewrite of documentation. I'm not
>>     proposing an
>>     > effort to systematically restructure existing route relations into
>>     > subrelations and superrelations. However, this documentation would
>>     > better support mappers who are interested in carrying out such
>>     > improvements themselves. Thanks for your attention.
>>     >
>>     > [1]
>>     >
>>     https://lists.openstreetmap.org/pipermail/talk-us/2013-November/thread.html#12165
>>
>>     >
>>     > [2]
>>     >
>>     https://wiki.openstreetmap.org/wiki/Highway_Directions_In_The_United_States
>>     > [3]
>>     https://wiki.openstreetmap.org/wiki/User:Minh_Nguyen/Route_directions
>>
>>     -- 
>>     minh at nguyen.cincinnati.oh.us
>>
>>
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>>
>>
>> -- 
>> @osm_washington
>> www.snowandsnow.us <https://www.snowandsnow.us/>
>> OpenStreetMap: Maps with a human touch
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>

-- 
Minh Nguyen<minh at nguyen.cincinnati.oh.us>
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