[Talk-ca] Route reference tagging: time for change?

[Brian M. Sperlongano]

Greetings from south of the border.

I've been doing considerable work recently to improve vector tile
renderings for highway shields and highway concurrencies (multiple routes
on the same route).  You can see some of the ongoing work on an open GitHub
ticket[1] and related issues in OpenMapTiles.  We've made a lot of progress
recently, and accurate highway shield rendering is an important rendering
concern in the US mapping community; I assume Canada is similar in that
regard.

(the descriptions below apply to OMT vector tiles, other renderers may
differ).

The first thing I should note is that, in OMT, if a way is a member of a
route relation (with a network and ref set on the route relation), whatever
is in each way's ref field is completely ignored in favor of what's in the
route relation.  So, as long as route relations are established, it really
doesn't matter what's in the way's ref tag.  There has been some discussion
of using the way ref tags for determining the order of routes in a highway
concurrency, but that's somewhat hypothetical as the format of indicating
concurrent route refs isn't standard and requires fuzzy matching.

Additionally, if there are unsigned routes or portions of routes (which are
definitely a thing in the US, not sure about Canada), it's really helpful
to put unsigned_ref tags on the ways and/or relations so that a future
renderer can suppress rendering of shields for these routes.  Nothing
parses these unsigned routes yet, but it's something we're talking about
and hope to have a solution for.

Lastly, I'd like to point out the current OpenMapTiles code for determining
whether a route is part of the Trans-Canada network is tremendously
complex, and includes name matching as well as checks for specific refs:
https://github.com/openmaptiles/openmaptiles/blob/1b0b1fd12131167904b61628c1ea403359f4a6e7/layers/transportation_name/update_route_member.sql#L36-L47

I'm not sure if the current state of Canadian route tagging has changed
since that code was written, but it seems to indicate significant
inconsistencies in route network tagging.  Be aware that changes to how
routes are tagged DOES impact renderers and those changes should be
advertised and hopefully documented somewhere for renderer authors.

In short: anything that makes route / network / ref tagging consistent is
really helpful to renderers in providing clear rules, with accurate and
consistent route networks being the most important piece of data.

Significant discussion on highway shield rendering and the ongoing
OpenMapTiles work is happening on the OSM US Slack, channel
#american-map-style.

[1] https://github.com/openmaptiles/openmaptiles/issues/1128

On Sun, Jul 4, 2021 at 2:52 AM Jherome Miguel <jheromemiguel at gmail.com>
wrote:

> I’ve been considering a major change to the way we tag highway ref=
> values, trying to follow the lead with our neighbours stateside.
> Currently practice has been to use bare route numbers except in Manitoba,
> where the number is preceded by PTH, PR or Route depending on type of
> route; for the data user’s end, the rendered shield is generally dependent
> on the tagged classification of the road (mostly tied to the road’s
> official classification by the provincial or territorial transportation
> ministry), the province or territory, and the network tag in the route’s
> relation.
>
> The proposal for route numbers is, by type of road:
> - For provincial and territorial highways, add province/territory postal
> abbreviation before number (e.g. AB 2 for Alberta Highway 2, ON 401 for
> Ontario Highway 401, BC 5 for BC Highway 5, NS 101 for Nova Scotia Highway
> 5), except perhaps Manitoba provincial highways (can keep ref=* with PTH
> for provincial trunk highways including the Trans-Canada and the
> Yellowhead, and PR for provincial roads). This includes routes with special
> shields different from provincial or territorial towns standard designs
> (e.g. the TransCan, BC Highway 5 as the South Yellowhead, the Mackenzie
> Highway). The QEW will remain as it is. For highways forming the TransCan,
> it can be tagged as a second ref= value, as TCH.
> - For Ontario regional and county roads, add CR or RR before number
> depending on the type of municipality the road is in.
> - For Toronto expressways (the Gardiner, the Allen, the DVP), there will
> be no changes.
> - For Winnipeg city routes, there will be no changes.
>
> Any further ideas? Comments?
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