[OSM-talk] Classifying Ways worldwide (was: Numbers and i18n)

[Collinson Mike]

I've been a passive member of OSM for over a year now and feel that 
over the last few weeks it has moved from being a purely experimental 
UK-centric system to being a (the!) working worldwide repository of 
open source street map data and of collaborative standards.  I've 
therefore spent a few days to add all my accumulated collection.  On 
that experience, I feel the one big difficulty I still have as a 
beginner is how to systematically describe the Ways that I make in 
terms that can be easily used by other members to make maps, 
navigation systems and hopefully to show more information on the 
www.openstreet.org main page map itself.

I'm therefore very interested in a suggestion made by Wollschaf  a 
couple of days ago and feel it is very elegant, so add some arguments 
in favour of it.  It solves a number of problems for me mapping 
outside the UK and is flexible enough to create a set of "starter" 
tag values for beginner's to use and still be useful for complex 
situations and new uses.

The essence of what Wollschaf said (below) was: use two tags, one for 
the administrative classification and one for the physical:

waytype=A (2 lanes+ 1 breakdown lane on a motorway, or very wide road)
waytype=F (1 lane, wide enough for a car)
wayclass=uk:primary
wayclass=uk:motorway
wayclass=de:autobahn
wayclass=de:bundesstrasse
wayclass=au:stateroute_a (Single carriageway interstate or 
interregional primary highways)
wayclass=au:expressway

and I'd add a "global" generic wayclass value set that should be as 
small as possible and non-overlapping but allowing personal 
common-sense judgement:

wayclass=expressway or 1 (typically dual carriageway freeway with use 
restrictions)
wayclass=primary or 2 (typically arterial and/or heavily used sealed 
dual or single carriage way used by long distance traffic or major 
cross-town traffic within cities)
wayclass=secondary or 3 (typically reasonably good quality single 
carriage way roads [sealed or unsealed according to local custom] 
linking smaller towns, moderate traffic)
wayclass=minor or 4 (local use only, ordinarily little traffic)
wayclass=access or 5 (generally short access roads to/in residential 
areas, industrial estates, commercial forests, fire trails, tourist 
features, expressway service centres etc)

Why I like it:

(1) Not everywhere has a classification system.  I'm mapping in the 
Philippines which has no publicly visible road classification system 
at all that I'm aware of.  Using the current system means that I'm 
assigning 'highway=' classifications based purely on personal 
judgement and whim.  I think that is the most powerful argument for 
having both tags.

(2) Administrative classification systems vary. I'm also mapping in 
Australia which has a relatively complex administrative 
classification of National Routes, Metroads, State Highways M, A, B, 
C, D, Tourist Drives with State variations, 
(http://en.wikipedia.org/wiki/Australian_highways).  Mapping the 
current 'highway='  values is possible but only approximate and may 
differ from person to person.  The current system needs internationalising.

(3) Being accurate and informative with the data available.  I wonder 
if I'm not alone in not scrupulously recording the administrative 
classification of a road? Indeed it may not be displayed on road 
signs?  At the moment I have to guess or leave 50km+ lengths of road 
with no clue to map makers about how to display it.  With a 'waytype' 
parameter I can easily remember the width of road and assign 
accordingly.  Therefore a useful descriptor can always be captured.

(4) Beginners.  It has taken me a year to be confident about entering 
Ways that might be meaningful to map makers, thanks to 
http://wiki.openstreetmap.org/index.php/Map_Features - but I still 
scratch my head in many situations.  I'm still rather at sea when it 
come to practicality for navigation software.  With the proposed 
system, I think it would be very easy to instruct a beginner:
         - Enter nodes, join them up as segments and mark one-way segments,
         - then map your road names over the top as Ways,
         - enter the 'name' of your Way and what 'waytype' you 
observed it as being,
         - *If* you know the classification, add the 'wayclass' too.
         - If you want to go further, refer to xxxxx.
Easy!  A low entry barrier and will result in data that can be 
displayed in a meaningful way.

(5)  Type and class can complement each other for display and 
navigation purposes.  As an example, Sydney has lots of alleys - very 
narrow metalled through tracks often providing access to the rear of 
buildings which are clearly worth flagging to route navigation 
software as something worth avoiding and missing out or 
de-emphasizing on map displays.  Using the current 'highway=' 
classification, I feel I can only mark them as ''minor', 
'unclassified' or 'residential'.  Unfortunately I have exactly the 
same choice for the nice wide residential streets around about.  So, 
either I invent a new 'alley' classification that may not be 
understood in all cultures or I simply mark it as 'residential' with 
a 'waytype' to show it as very narrow.

(6) Elegant. Using 'waytype' and 'wayclass'  seems very elegant and 
simple to me.  Self-obvious and obviously relates to the usual parent 
Way.   It gets rid of the UK-centric 'highway' definition. I am 
British but it has no or different meaning outside that country and 
pedantically not really within it, (what about "Byways"?).

(7) Easily backwards compatible.  Take 'highway' key, rename it 
'wayclass' and either put 'uk:' in front of the current tag values or 
convert them to a smaller global set.

Variations

One alternative mentioned using numbers could also be combined:

wayclass=1

where 1:
uk:motorway
de:autobahn
etc

I think this has merit from an internationalisation point of view 
(map making software won't have to have built in tables of all the 
international variations) but may be dangerous when there are 
mismatches between countries.  I can't think of a good example - 
perhaps there are none - but as  a thought experiment would a UK 
motorway be mapped to a US Interstate Freeway or to a State Freeway?

Drawbacks?

The only potential drawback I can see so far is to the 'wayclass' in 
that in some countries, roads can have more than one administrative 
classification.  In the US, as I recall, roads can have both 
Interstate and State designations That problem though may be more for 
the 'ref' tag to sort out, the 'wayclass' would just take the more 
important one as a single value.

Mike


At 09:56 PM 31/07/2006, Wollschaf wrote:
>On Mon, 31 Jul 2006 11:50:44 +0100, Etienne wrote:
>
>
> > I think in this context (Street Maps) we should really be considering
> > administrative classifications.  OSM can accommodate physical
> > characteristics but that, to me, seems secondary for the most common kind
> > of uses of OSM data.
>
>In my opinion it is important to have both. Route planning software can
>make better decisions if the physical properties are known. Looking at
>maps.google.com (teledata maps) in my area, there are so many roads
>rendered as if you could actually drive on them. In reality, you can't -
>one car coming from the other direction and both are terribly stuck. Using
>my route planning software, I've been sent through vineyards several
>times. Usually, bigger roads were nearby that obviously were classified
>the same way, perhaps as minor. Currently, I can't do better in OSM.
>
>What should I tag a secondary road with that's several times bigger and
>faster to drive on than the primary road nearby, thus clearly being the
>preferred way to travel?
>
>I think we need two sets of tags: one for physical properties and one for
>the administrative classification, based on a scheme for every country.
>This way everything can be tagged. Not every country is as ordered as we
>are used to. I have severe trouble to fit the current highway values to
>the roads I created in Sardinia, Italy. A lot of interpretation is needed
>to fit the tags to the roads, and by reading a map created out of the
>guesswork misunderstandings will occur.
>
>To make OSM better than commercial map suppliers, we need as much metadata
>as we can get. Physical road properties will definitely improve the maps.
>
>Examples for a separated way classification:
>
>waytype=A (2 lanes+ 1 breakdown lane on a motorway, or very wide road)
>waytype=F (1 lane, wide enough for a car)
>wayclass=uk:primary
>wayclass=uk:motorway
>wayclass=de:autobahn
>wayclass=de:bundesstrasse
>
>Administrative classification could then also be used to set permissions
>and speed limits, which is currently not possible because of the diversity
>of rules in different countries.
>
>Perhaps the tag values should be all in english, to improve readability. I
>would not want to write software using all these tags without
>understanding the language behind. The tag value names are not as
>important as the correlation... numbers are sufficient, but hard to
>remember.
>
>Wollschaf
>
>**wondering now about highway=us:highway, and why whether just to remove
>the high in way to make more sense. We're just dealing with ways, aren't
>we?
>
>
>
>
>
>_______________________________________________
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>talk at openstreetmap.org
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