[Talk-us] Ref values on unusual highway networks

[Brian M. Sperlongano]

Good morning,

As the openstreetmap-americana project[1] continues its march through the
addition of highway shields to the map, we have quickly encountered, as any
American roadgeek might expect, the long list of unusual or one-off highway
networks.  In addition to presenting an artwork challenge in squeezing
questionable state DOT graphic design choices into a 20 pixel icon, we are
also encountering a fair amount of variety in how or whether ref values are
tagged on these routes, and in some cases the routes lack a route relation
entirely.  We initially encountered this when discussing how to draw
shields for Kentucky's parkway system[2], but there are quite a few other
route networks that are similarly borderline cases.

I've begun the following wiki page to compile a listing of this rogues
gallery of road networks which do not have a clear translation between
signage and ref values:

https://wiki.openstreetmap.org/wiki/United_States/Unusual_highway_networks

So first off, if you know of other unusual highway networks that don't have
straightforward mappings to ref values, please add them, as it forms a
helpful "TO DO" list for the project to add renderer support.

There have generally been two approaches to assigning ref values for these
cases:
1. Omit the ref value entirely
2. Create the ref value from an initialism of the route's name (for
example, Sam Houston Tollway is tagged ref=SHT and I am not making this up)

Perhaps the most borderline case is of New York State's green-signed
parkways, which feature the parkway name in drop-caps, where the first
letter is drawn in much larger text.

There has been a fair amount of discussion about these manufactured ref
values, and whether they should be removed from these route relations, with
examples given about how they cause undesired behavior by data consumers
such as turn-by-turn routers that expect the ref tag to contain text
displayed on signage as a route number.  Some have surmised that these ref
values were likely added to cause osm-carto, which of course does not
render highway shields, to add a label lozenge.

Community input is requested on the question of where we should draw the
line between what is properly tagged as a ref and and what should be
omitted in these cases.


[1] https://github.com/ZeLonewolf/openstreetmap-americana
[2] https://github.com/ZeLonewolf/openstreetmap-americana/pull/119
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