[Tagging] Classifying roads from Trunk to Tertiary and Unclassified

[Joseph Eisenberg]

We recently discussed the confusion about unclassified vs residential
recently, but a more significant issue is that different countries and
regions have a wide variety of practices about assigning the major
highway classes, especially trunk and primary.

In some countries, including parts of Europe and parts of the USA,
highway=trunk is reserved for "expressways" or "motorroads" with
certain physical characteristics. However, in England where the tag
originated, highway=trunk is used for the main, non-motorway highways
in the country. As can be seen by glancing at the rendering of
England, these highway=trunk connect just about every place=town in
England: https://www.openstreetmap.org/#map=6/53.021/-1.033

This means that highway=primary and highway=secondary is used for most
other paved roads with one lane in each direction. Many place=villages
in England are connected to a  highway=primary and the rest have a
highway=secondary. And most hamlets are on a highway=tertiary which
connects to larger villages or a town.

This leaves highway=unclassified for very minor roads, often too
narrow for 2 wide vehicles to pass each other, connecting isolated
dwellings and farms. This is how they are like residential roads, in
the English system.

I would like to adapt this system to Indonesia, where the government
has not yet classified most roads below the National level, but the
"Jalan Nasional" class of major highways has already been decided to
be mapped as highway=trunk.

See https://wiki.openstreetmap.org/wiki/Indonesian_Tagging_Guidelines#Roads
for an attempt.

The idea is that one can determine the classification of highway based
on what size of settlements it connects:

trunk - connects cities to cities ("National Roads")
primary - connects a town to a city or another town
secondary - connects a village to a town/city or another village
tertiary - connects a hamlet to a village/town or another hamlet
unclassified - connect farms / isolated dwellings to a hamlet/vilage
or another farm.

This system is internally consistent and works well for rendering, as
well as for routing.

Thoughts?
- Joseph
(I wish I could review this with other Indonesian mappers, but we
don't have an active forum or mailing list)