[Talk-us] State highway refs (was Re: New I.D Feature)

Minh Nguyen minh at nguyen.cincinnati.oh.us
Sun Nov 30 08:35:35 UTC 2014

On 2014-11-29 22:45, Shawn K. Quinn wrote:
> On Sat, 2014-11-29 at 22:21 -0800, Minh Nguyen wrote:
>> Do any routing engines currently care about prefixes on way refs?
>>   From what I've seen so far, most of the map styles that use the ref tag
>> to distinguish route networks will recognize either the state
>> abbreviation, "SR", or "SH". Some renderers use the prefix to choose a
>> state-specific shield, assuming any unrecognized prefix is for a county
>> route (white rectangle at higher zoom levels). MapQuest only recognizes
>> state/provincial abbreviations. Not that we should place too much stock
>> in individual renderer decisions. :-)
> OSRM doesn't know that, for example, TX 6 and SH 6 are the same highway.
> Once upon a time, I'd get directions that had things in them like:
> Turn right on TX 6
> Continue on SH 6
> Continue on TX 6
> Continue on SH 6
> Continue on TX 6 ... etc
> Granted, OSRM still doesn't handle it gracefully when another highway
> multiplexes for a stretch, but at least one might be able to figure out
> which highway one's supposed to stay on when it's ref'd the same across
> the board. When it's not, it becomes much trickier.

That's a good point: it is certainly important that an individual route 
or road be tagged consistently, both its ref and (to the extent 
possible) its name, so that routers and tools like Nominatim can 
aggregate ways into roads.

minh at nguyen.cincinnati.oh.us

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