[Tagging] capital and state_capital: how are they being used in your country?

Fernando Trebien fernando.trebien at gmail.com
Thu May 15 19:08:37 UTC 2014

On Thu, May 15, 2014 at 3:01 PM, Colin Smale <colin.smale at xs4all.nl> wrote:
> It is not actually an attribute of the place at all, because if you
> moved the place to e.g. the middle of the Atlantic Ocean it would no longer
> be a capital. It is an attribute of the relationship between the place and
> an (administrative) area. So the place and the area (represented by a
> relation in OSM) may reference each other, for example by including the
> place in the relation with a role such as admin_centre. Because a place
> cannot be a capital in and of itself (it can only be a capital OF somewhere)
> putting these tags on the place node is a denormalisation - to make things
> more convenient for the data consumers, so they don't have to go through the
> relations to see if a place is a capital or not. Such denormalisations are
> not always a Bad Thing (it's a balance), but there must be an acceptance
> that there is only One Truth, and zero or more derivatives. The One Truth
> would be in the relations and we will need a mechanism (or at least an
> algorithm) to derive the tagging for the place from the relations which
> reference it.


Note: because apps need to support certain kinds of relations (turn
restrictions, multipolygon rendering, etc.), it "should be easy" (as
far as I can imagine the algorithm) to extend such support (without
sacrificing performance) to figure out whether a city is a capital by
reading the list of members of the relations the city's node is a
member of.

> capital=2 only means it's the capital of A country. Without a link to the
> country in question, this tag could be misused to increase prominence on the
> maps, AKA "mapping (incorrectly) for the renderer", which is "frowned upon".


> So I say let's ban capital=* and admin_level=* on the place nodes!

I tend to agree, and I don't see yet any practical situation where
using those tags is absolutely necessary and reading from a relation
is not possible/too difficult.

> Colin.
> On 2014-05-15 19:36, fly wrote:
> Am 15.05.2014 18:32, schrieb Andreas Goss:
> Am 5/15/14 16:30 , schrieb fly:
> Regarding the original discussion I am in favour of using capital=[2-10]* if
> an additional tag is needed.
> I meant additional to the roles for the boundary relation above (cutted).
> admin_centre for 1 or more nodes
> capital if not equal to admin_centre or more than one admin_centre present.
> The semicolon (;) is defined as value separator so we could have
> capital=4;6;8 or similar.
> This just sounds like a disaster waiting to happen. I also don't see why it
> would be needed. You are doubling the risk of errors when it comes to
> admin_levels. Now you don't just have to ensure all relations are correct,
> but also all nodes.
> As we are talking about admin_level (<-> capital) on nodes and it was
> mentioned that it might be easier to use and I am not sure if it is used.
> If any I would go with capital=* and not admin_level=*
> You also have no reference to those numbers. When you add one admin_level to
> a relation that relation has a name (Bavaria is a state). When placing
> admin_centre you know the name of the relation and of the city so you can
> make a connection (Munich is the capital of Bavaria). And while that maybe
> is obvious at level 2 and 4, it becomes more compicated when you get into
> smaller administrative areas. This also makes it more complicated to find
> errors in the first place. I also bet that people are going to assume that
> some numbers are missing and are simply going to add them, especially as it
> varies from country to country, from state to state etc. Others might simply
> add a number with good intend, because they had the wrong admin_levels in
> mind.
> Cheers fly
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Fernando Trebien
+55 (51) 9962-5409

"Nullius in verba."

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