OpenStreetMap

Doing an A-road as a relation

Posted by mwbg on 28 June 2013 in English (English)

I've just noticed, in my bus-routing activities, that someone has apparently created a relation representing the A38. Err, why ? That info can be derived directly from the map and every road segment in this country is supposed to have exactly one road number/letter, isn't it (with no sharing). Would I be right in deleting this relation ?

Location: Ripple CP, Malvern Hills, Worcestershire, West Midlands, England, United Kingdom

Comment from cartinus on 28 June 2013 at 13:20

While I too think those route=road relations are completely useless nonsense, there are a lot of people actively creating and maintaining them. So deleting the relation is not a good idea. Completely ignoring it is however fine.

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Comment from Richard on 28 June 2013 at 15:57

Yup, route relations have no purpose in Great Britain. In other countries, where roads can share a number, yes, they are useful. But here they're simply a hindrance - yet more one thing to confuse the newbie mapper.

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Comment from Pink Duck on 28 June 2013 at 16:39

What about two A-roads that share a roundabout? ref=A1;A2 on the roundabout or separate relations for the references?

It is somewhat easier to visualise a relation online than the aggregation of highway ways within a bounding box with a certain tag.

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Comment from mwbg on 28 June 2013 at 17:19

@PinkDuck. I must admit I hadn't thought of the roundabout question.

I have been led to believe that each and every road segment in the UK has no more than one letter-number. There are numerous examples of e.g. where two A-roads go through a single thoroughfare in a small town, but where that thoroughfare has just one of the numbers, with the "other" road disappearing on one side of the town, only to restart on the other side. I've only ever once seen an A-road marked as Axxx/Ayyy on the ground.

So, given the choice, in your example, I'd leave the roundabout unnumbered, with two disjoint segments of road either side. The plotting of a continuous representation of the "Axx" should be done at rendering level.

I think there is very little point in maintaining a relation where that information could be unambiguously derived from the map; it's just one more thing that people have to (but shouldn't) fix if they, for example, add extra bend points to a road's geometry.

I will leave extant relations of this nature alone. I won't delete them, but I won't go out of my way to maintain their continuity should I have cause to, for example, retag a road due to the council renumbering a section of road (such as downgrading the A999 to the B9990).

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Comment from Richard on 28 June 2013 at 17:34

Standard practice in the UK is indeed to leave roundabouts un-ref'd.

@PinkDuck: indeed most current tools do make it easier to show a relation than the set of ways with a certain tag; but as a general rule, since mappers are our most precious resource, we optimise for the mapper. That means not adding duplicate information where there's no need to do so. :)

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Comment from Pieren on 1 July 2013 at 09:24

Same in France. Roundabouts belongs to all related routes and then, have either all references or none. For simplicity, we choosed 'none' as we consider a roundabound as an inflated intersection node (and you don't ask the question when the intersection is a node). We also try to follow the KISS principle about relations and create them only when we have no alternatives. Unfortunately, some people tend to use relations to make their software applications/visualisations easier. And delegates the difficulties of creating and maintaining relations to the crowd.

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