[Tagging] Road hierarchy

Mark Wagner mark+osm at carnildo.com
Sun Aug 4 19:38:41 UTC 2019

On Sun, 4 Aug 2019 09:35:41 +0300
Tomas Straupis <tomasstraupis at gmail.com> wrote:

> Hello
>   Road hierarchy is needed for a number of things:
>   * deciding which classes of roads to display on different scales in
> a map
>   * performing road network validation
>   * other tasks (f.e. typification of buildings - orientation)
>   Hierarchy would be different in different context: motorcar,
> bicycle, pedestrian etc. For the time being I'm only asking about
> motorcars.
>   There is non written (or I could not find in wiki) or "de facto"
> hierarchy:
>   * motorway
>   * trunk
>   * primary
>   * secondary
>   * tertiary
>   * unclassified
>   * residential
>   * living_street
>   In some regions unclassified has a higher position in hierarchy, in
> other regions unclassified, residential and living_street have the
> same position. This is fine for the time being.
>   I'm also intentionally skipping _link classes.

The hierarchy is 

* Trunk
* Primary
* Secondary
* Tertiary
* Unclassified/Residential are more or less at the same level.  They're
  minor enough that any difference between them is a matter of local
  opinion.  In general, if you want a complete-looking map, you should
  draw both or neither.

Motorways are defined by their construction standards or legal
classification: think the Autobahn in Germany or Interstates in the US.
They're effectively at the top of the hierarchy, but this is an effect
of the things that make them motorways, not the cause.

Tracks, service roads, and living streets are outside the hierarchy.
Like motorways, they're defined by their attributes, not their
importance, though in this case, the effect of those attributes is to
tend to put them at the bottom of the hierarchy.

Deciding when and how to draw them is a matter of the needs of a map:
for example, a mountain-bike map for US National Forests might
emphasize tracks over hierarchy roads, while a driving map for farm
country might omit them entirely.


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