[Tagging] Road hierarchy

Florian Lohoff f at zz.de
Sun Aug 4 13:37:52 UTC 2019

On Sun, Aug 04, 2019 at 11:20:49AM +0100, ael wrote:
> > For me unclassified is the same as residential. The difference is that
> > unclassified is for interconnecting residential areas, and residential
> > has residential traffic. So for me there cant be an unclassified within
> > city boundaries, and as soon as there is predominent residential it
> > cant be a unclassified.
> How have you come to that conclusion? It flatly contradicts the normal
> meaning. Perhaps your local area uses the term "unclassified" in a way
> different from the OSM convention?

A residential is also an unclassified road. It does not have
a classification as a tertiary or primary. So the difference
between an unclassified and a residential is not by their
classification (or lack thereof).

Their difference is usage. In case of residential its usage is
predominantly access to an residential area, whereas the unclassified is
for interconnecting residential areas (be it villages).

This is the exact terminology from:


	"The tag highway=unclassified is used for minor public roads
	typically at the lowest level of the interconnecting grid network.
	Unclassified roads have lower importance in the road network than
	tertiary roads, and are not residential streets or agricultural tracks.
	highway=unclassified should be used for roads used for local traffic,
	and for roads used to connect other towns, villages or hamlets.
	Unclassified roads are considered usable by motor cars. Public
	roads of low importance within town and cities that are not residential
	may also be highway=unclassified."

So the difference is purely on the usage for residential traffic.

My assumption is that within city boundarys ALL roads carry mostly
residential traffic. One could argue that some roads are carrying
more through traffic than others but where do you draw that line and
do you count traffic when mapping? Its something we as OSM can 
not observe on the ground. Its a statistical matter.

Another indicator for me that neither unclassified nor residential
are of higher priority is the handling in for example OSRM. It
treats both equally in the assumption for travel speed etc.

This is why i make the shortcut in using residential within city
boundarys, and unclassified outside of city boundaries where there
is no residential usage - because everything else is highly disputable
and only provable with traffic analysis and statistics.

Florian Lohoff                                                 f at zz.de
        UTF-8 Test: The 🐈 ran after a 🐁, but the 🐁 ran away
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