[OSM-talk-be] some thoughts and remarks about border mapping

[Lennard]

Ben Laenen wrote:

>> The Dutch border system as it is now is comprised of overlapping ways
>> using shared nodes.
> ugly :-)

Relations were non-existant during the time of the AND import. I guess 
this was the only thing that could be done back then. It also ensures 
that no matter which admin_level you extract, you have closed borders.

> but I remember seeing a relation on the country border, so how's that 
> used?

Don't know. Maybe someone was experimenting already? Where was this?

>> The municipal border is a closed way, the 
>> province border is another closed way, and it shares the nodes with
>> various municipal boundaries. And on a higher level, the national
>> border is another closed way that shares the nodes with the
>> respective provinces and municipalities along the border.
> 
> How do they do it in Baarle-Hertog/Nassau?

I shudder to think. :)

Can't check, cause the API is down right now, but I assume it uses 
another bunch of closed ways, probably 2 stacked on top of each other, 
since all those boundaries are all part of the border between Antwerpen 
and Noord-Brabant, and Belgium and The Netherlands.

> Short answer: no, I think you need all rendering rules yourself. 
> However, it should be quite easy.
> 
> Just need to go to the whole proposal phase once...

Once this is fully supported, I think the whole of the NL border system 
needs a conversion. And I can start to collect all the tiny fragments of 
municipal borders I find in Oost-Vlaanderen together in proper 
relations. Okay, I can already do that last bit, but I still need to 
keep the admin_level on the ways themselves.

> btw, the relation way may need one extra thing: a "left" or "right" role 
> for the members telling on which side the entity is. I think it's 
> needed for solving ambiguity, especially with ex- and enclaves.

Very smart thinking, especially in cases where only fragments have been 
mapped, or the border is not predictable (as a roughly circular area 
around a town). And another reason to be very very careful when 
reversing ways in editors that do not fully process relations yet.

-- 
Lennard