[OSM-talk] Proper tagging of multi-admin_level borders (Was: National borders in the British Islands)

[Ben Laenen]

On Wednesday 18 June 2008, Dylan Semler wrote:
> On Fri, May 30, 2008 at 11:27 AM, Martijn van Oosterhout
> <kleptog at gmail.com>
>
> wrote:
> > - admin_levels nest, so that the area covered by an admin_level=X
> > is also covered by areas with admin_level > X
>
> I just want to verify that I interpret this correctly because I
> haven't found it documented anywhere on the wiki.  What is the proper
> tagging prodecdure for high-level borders like country borders that
> are also borders of states, provinces, counties, etc.?
>
> I can imagine the following options:
> a) One way tagged with the lowest number (highest administrative
> border) b) One way tagged with several admin_levels, one
> corresponding to each border that is present
> c) Several ways on top of each other, each tagged with one
> admin_level
> d) other? 
>
> I think (a) is the cleanest and can still offer all of the necessary
> information.  What is the concensus?

I think relations will be the only solution here. There's no guarantee 
that a border of admin-level 5 is also a border for admin-level 7 for 
example. So I'd think the best way is to have ways for each boundary, 
and then combine all boundaries together in one relation which has the 
admin-level. So one boundary way can belong to many admin-level 
relations like that.

Greetings
Ben