[OSM-talk] Administrative boundaries export

César Martínez Izquierdo cesar.izq at gmail.com
Thu Oct 3 09:35:43 UTC 2013

Thanks for all the advises and suggestion. I agree that in order to achieve
this, at least 2 tables/trees/dbs have to be maintained:

1 - The relationship of each admin_boundary on a certain level with its
parent (and the opposite) and whether this same boundaries applies for
other admin_boundaries (as suggested for some areas of Germany)
2 - For each country, how to distinguish the land mass from territorial
waters. I am more interested on mapping the land mass, but the territorial
waters could be also generated if we have this distinction.

Regarding 1, I think it would be reasonable to try to codify it within OSM
(for instance using is_in tag), but I think the tagging scheme should be
further developed to correctly capture all the information we need, so I
will generate an external table/database instead. Probably, a table per
admin_level containing relation-id, ISO 3166 code would be enough (but I
have to study what should be used for deeper subdivision levels), as it
will contain the father-children relationships and also would solve the
problem with a boundary being the same for different admin_levels. The
algorithm could check against OSM data for code and for relation-id when
missing, and report any added or removed boundaries compared with previous

Regarding 2, for the long term I thing separate relationships should be
present in OSM for land mass and territorial waters (this also involves
clarifying the tagging scheme), but for the moment I will try to manage
with existing tags.

I assume it will not be a small task, so I will try to be pragmatic and
start exporting "what can be exported using a straightforward way" and then
refining the approach little by little. Probably, in order to refine these
approaches it would be helpful to have some viewer similar to the one on
openstreetmap.fr (to easily see what should be corrected on OSM data or on
the extraction algorithms), but for the moment this is outside of my plans.

I expect results on the scale of months/years rather than days/weeks
(according to my planned dedication), but I will keep you informed when I
get some news.

Eugene, I am also interested on your proposal to store on Wikidata a
table/database similar to the one described on 1, so any further details on
available infrastructure, technologies in use, work already done, etc are


César Martínez Izquierdo

2013/10/3 Eugene Alvin Villar <seav80 at gmail.com>

> On Thu, Oct 3, 2013 at 6:52 AM, Christian Quest <cquest at openstreetmap.fr>wrote:
>> UK level 4 is on the maritime borders (island culture ?) where most other
>> European countries stop on the coastline... tagging bio-diversity is not
>> helpful !
> This is actually another point to consider when extracting admin
> boundaries from OSM data.
> My personal view is that the admin boundary marks the boundary where the
> administrative entity exercises jurisdiction. Under UNCLOS, nations are
> allowed to exercise full sovereignty over internal waters (which includes
> water seaward of the coastline but within the baselines) and almost full
> sovereignty (foreign ships are allowed "innocent passage") for territorial
> waters (up to 12 nautical miles from the baselines). So I think that using
> the maritime boundaries as the admin_level=2 boundary is not incorrect and
> this is reflected in OSM.
> Use of maritime boundaries for admin_level=3 and higher (such as with UK)
> depends on how the particular nation interprets its internal
> maritime/fisheries laws. In my country, we have "municipal waters" which
> can be up to 15 kilometers from the shoreline and that's where
> municipalities can exercise jurisdiction.
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   César Martínez Izquierdo
   GIS developer
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   ETC-SIA: http://sia.eionet.europa.eu/
   Universitat Autònoma de Barcelona (SPAIN)
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