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

Colin Smale colin.smale at xs4all.nl
Thu May 15 18:01:22 UTC 2014


Tagging capital=* or admin_level=* on a place is IMHO not to be done
lightly. 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. 

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! 


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

admin_centre for 1 or more nodes
capital if not equal to admin_centre or more than one admin_centre

>> 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

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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