[OSM-talk] Long Ways and API 0.6 - multirelations

Dave Stubbs osm.list at randomjunk.co.uk
Mon Feb 9 10:14:27 GMT 2009


2009/2/9 Frederik Ramm <frederik at remote.org>:
> Hi,
>
> marcus.wolschon at googlemail.com wrote:
>>>
>>> You need the route relation so you can represent easily both a local
>>> and international route over the same ways, but it's no big deal if
>>> you have to split the 420km international route into three sections.
>>
>> Do you have a wiki-page that defines how these multi-relations are
>> to look like and what the exact semantics are?
>> My software works well with some relations but has no support for
>> such multi-relations yet.
>
>
> I don't think Dave was thinking of anything more than two different
> relations (partly) using the same ways. That would not warrant any special
> kind of relation.
>
> For situations in which you want relations contained in relations - e.g. in
> a situation where a nationwide cycle route comprises 5.000 ways and thus
> cannot be expressed in one single relation -, what I suggest is creating a
> number of "sub relations" that are members of a "super relation" with the
> same tags as the "sub relation". (The super relation might have a different
> "name" tag from the sub relations, in case you want to name your
> sub-relations "blah cycleway, southern section" or so).
>
> The "sub relations" will not receive any extra tags saying that they are sub
> relations.
>
> The "super relation" will not receive any extra tags saying that is is a
> super relation.
>

The main problem there is that you lose the super relation if it's
just made of sub relations. The map call won't return it, so you have
to know it exists and what its ID is before you can edit it. It's not
a problem for renderers or other planet processors as it'll be in
there. It might be a problem for people parsing country osms depending
on how your (and other) splitting tools handle it.




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