[OSM-talk] Map Features: Road classification schemes for worldwide use

[Etienne]

On 9/1/06, Wollschaf <mith at uni.de> wrote:
>
>
> As OSM grows bigger and attracts more users from all over the world, the
> current highway scheme to classify roads turns out to be too inflexible to
> be expanded adequately. It is also misleading to combine physical and
> administrative / logical properties in one tag, especially if the tag is
> used for more than one country. Given the fact that creating an own set of
> highway values for every country is too much work, too hard to adapt for
> foreign mappers and - most importantly - not at all being easy to render,
> a new scheme has to be found that can be applied universally.
>
> Several users outside the UK can't tag properly, I for one need a set of
> tags to describe roads I mapped in Sardinia, and the highway scheme simply
> does not fit. So I think this issue is of a certain importance.
>
> After some thinking and discussion, the following facts emerged:
>
> - Some countrys do not have an official road classification scheme.
> Forcing users to fit roads into another scheme is not very good.
>
> - Almost every country has a (slightly) different scheme. There are too
> many countries to create a unique scheme for every country and have route
> planning / map rendering software cope with that.
>
> - Physical and administrative / logical properties should be separated
>
> - Putting several physical properties into one scheme is not flexible
> enough; Each physical property should get its own tag.
>
> - A scheme to classify common roads that simply implies several physical
> properties that can be overridden by their respective tags facilitates
> tagging and storage requirements.
>
> - Compatibility with existing tags is necessary; Automatic conversion or
> addition of the new tags is a possibility once a draft has been finished.
>
> If I forgot something, please add it.
>
> I have put two pages in the wiki that can serve as basis to discuss and
> develop a more universal scheme to classify and describe roads.
>
> Physical road properties:
> Worldwide road classification (physical)
>
> http://wiki.openstreetmap.org/index.php/Worldwide_road_classification_%28physical%29
>
> A main problem describing a road is that the width is hard to estimate. In
> my opinion it is far easier to remember and estimate road widh using
> vehicle units (car and truck widths). Software can still take default
> values for these "units" if a width estimate in metres is needed and a
> width value is not given. It is also far easier to comprehend that a road
> is wide enough for two cars to pass, but not for two trucks than a width
> value of four metres.
>
> I finally came up with a key named lane_layout (which may be renamed as
> soon as a better name is found) that describes each lane using a letter.
> Examples for normal roads:
> ...
> lane_layout="c" One lane; car fits on road, has to be slow
> lane_layout="C" One lane; car fits, enough space to open the doors ;)
> lane_layout="cc" Two lanes; a road where two cars can pass slowly
> lane_layout="CC" Two lanes; a road where two cars can pass without
> problems
>
> motorways:
> lane_layout="TTT" Three lanes; big enough for three trucks. It does not
> include permission for trucks to use all lanes, but the road is big enough
> to allow that physically.
>
> c and C stand for one car respectively - one for a narrow road and one for
> a normal one regarding a car. The same applies for t and T which stand for
> trucks.


Does C=t or is t>C?


For more than one-lane asymmetrical roads, left and right can be defined
> by segment direction. It is not necessary to allow asymmetrical roads, but
> it might prove handy to be able to describe those.
>
> An alternative to describe narrow roads is of course using a tag that has
> one of the values (very) narrow, normal and (very) wide. Very narrow for a
> truck is wide for a car, so essentially a reference has to be found. I
> think lane_layout is more flexible and precise in this respect, and
> essentially the same.
>
> A third alternative is to take fractions of lanes and define a road where
> two cars can only pass driving slowly by lanes=1.8; IMO it's weird and
> hard to remember.
>
> Perhaps somebody comes up with a better (more intuitive) scheme than mine.
> I will happily adopt it.
>
> Width values (measured) and approximate_width (estimated) are by no means
> obsolete, whichever way the intuitive classification is made; These keys
> will override the guesstimates given by lane_layout.
>
> Logical road properties:
> Worldwide road classification (logical)
>
> http://wiki.openstreetmap.org/index.php/Worldwide_road_classification_%28logical%29
>
> The main idea here is that each country has a classification scheme
> ordered by importance of the roads. It might be best to assign each
> logical road class a numerical value.
>
> Adapting to the uk-centric highway scheme, this could look like
>
> wayclass=1: motorway
> wayclass=2: trunk
> wayclass=3: primary
> wayclass=4: secondary
> wayclass=5: minor
> wayclass=6: residential
> wayclass=7: track
>
> (rename wayclass if better name at hand)
>
> The country using the scheme has to be defined, either in a separate
> country-tag [1] or in something like wayclass="uk:1"


Agreed this should be country specific.  To be more precise it is
administration specific.  New South Wales has a different set of road
classifications to Western Australia, for example.  In most cases there is
one scheme per country but there may be regional administrations that have
different rules.

In the UK the terms motorway, primary, secondary are well defined and fairly
well understood.  I don't see the need to code this using numbers,
especially as this would cause problems the moment some administration
decides to introduce some intermediate classification.  uk:primary,
uk:motorway etc would work for me.

Countries without motorways should have the possibility to add those
> values later, and start at a higher value / lower priority.
>
> Route planning software can then look at the priority and find routes with
> high efficiency.
>
> A default set for those values can be created and somehow restricted; If
> values 1 and 2 are reserved for dual-carriageway roads, the rendering of
> beautiful and meaningful maps will be pretty easy regardless of country. A
> wiki page can define and explain the numerical values.
>
> I hope that some useful ideas come up in this thread, as my brain is
> limited in its creativity and ability to solve this problem to everyone's
> complete satisfaction.
>
> happy mapping,
> Wollschaf
>
> [1] country tag can also be applied server-side to every node, segment,
> and way by excessive computation and a detailed world map. Being able to
> filter OSM data automatically by country sounds like a neat possibility.
>
>
>
>
>
>
>
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