[Tagging] Clarification unclassified vs residential

[Richard Fairhurst]

Florian Lohoff wrote:
> From the original meaning unclassified was the lowest class road 
> in rural or off city limits. residential was the lowest class road 
> within city limits. (Assuming that city limits mean residential 
> usage)

That's reasonable but not _quite_ true. highway=unclassified is often used
in urban areas to denote a minor distributor road. 

https://www.openstreetmap.org/way/145016745 is a good example
(https://goo.gl/maps/YUc6XfuA5wQ2 if you'll excuse the Google Street View
link). It's the distributor road for that estate, and of greater importance
than the largely cul-de-sac residential roads going off it; but doesn't have
a significant through-traffic purpose nor the engineering standards that
would imply highway=tertiary.

> [...]
> From OSRM profiles it isnt - So it doesnt make a difference for at 
> least OSRM.

OSRM's default profiles don't measure importance, only speed, and are fairly
blunt instruments which aren't used unmodified by anyone who's serious about
quality routing results. (Mapbox, OSRM's sponsors, override them with
traffic speed data, for example.) I wouldn't count them as a useful
indicator.

Richard



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