[Tagging] boundary relations and the subarea property

[Colin Smale]

Martin, 

I stated my point of view - I find it useful with clear added value. You
"don't see the point". Fair enough, we don't have to agree. Can you
describe some *real problems* the use of "subarea" causes? Can you
provide any *workable* alternative for the parties which DO support its
use? I thought that the "O" stood for "Open". Mappers who don't know
about it just carry on. Consumers/renderers who don't care about it just
carry on. Just moving its description/definition to the "Talk" page is
unlikely to change people's behaviour, realistically speaking. OSM data
will never be perfect, and both the data and every application which
processes OSM data is stuffed full of "workarounds" for quirks in the
data. 

Another reason it will never be perfect, is of course that we have no
way of quantifying the level of perfection. There is little consensus on
good vs. bad, or right vs. wrong. It might just be "good enough" for
various uses, and that's good enough for many people. 

//colin 

On 2015-11-27 10:04, Martin Koppenhoefer wrote: 

> 2015-11-26 20:24 GMT+01:00 Colin Smale <colin.smale at xs4all.nl>:
> 
>> I use the subarea member because it makes cross-checking easy. Have all the lower-level boundaries in my higher-level admin area been added to OSM?
> 
> what comes next? Have all the roads in a given administrative area listed with an "administrates" role in the relation? Cross-checking to me sounds like unhealthy redundancy here. It means having to do the work twice and having the information stored double.
> 
>> Unfortunately the various admin levels do not always form a strict hierarchy. A small area at (lets say) admin_level=10 might be enclosed spatially by entities at level 8, 7, 6, 5 etc but it only has a direct administrative relationship with one of them, which might not be the next-highest level (next-lower number).
> 
> in which way does a subarea role help here to solve real problems? Which administrative aspects/powers/relationships/fields are those that are looked at? Do you have concrete examples?
> 
>> Finding the boundaries of all districts within a county (UK example) becomes trivial with the explicit parent-child link.
> 
> yes, that's the one usecase that becomes easy. And all other mappers and users have to care for all those subareas and have their mapping more complicated just to facilitate this one usecase?
> 
>> Otherwise its like finding all boundaries with admin_level=8 which are at least 99% contained by the higher-level boundary. That sounds computationally a lot more complicated to me. Why not 100%? Because sometimes the boundaries at different levels are not imported/drawn from the same source, leading to the boundaries not being exactly coincident.
> 
> so because the data is not sufficently precise you decided not to fix the data but to keep separate hierarchy lists (aka relation membership) as a workaround? 
> 
> Cheers, 
> Martin
 
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