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

Frederik Ramm frederik at remote.org
Mon Feb 9 07:54:52 GMT 2009


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.

At some point in the future we might think about removing tags from the 
sub relations and assuming some kind of tag inheritance but I'd not like 
to over-specify that today.

For processing, I suggest that wherever a relation contains another 
relation and there is no special-case coding, the system should act as 
if all members of the sub relation were actually direct members of the 
super relation.


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