[OSM-talk] 12nm territorial borders - useful or rubbish?

M∡rtin Koppenhoefer dieterdreist at gmail.com
Mon Feb 14 17:00:47 GMT 2011

2011/2/14 Frederik Ramm <frederik at remote.org>:
> Maybe then we should only add this data where it has been changed by
> treaty/agreement? Much as most people don't bother adding maxspeed tags to
> every inner-city road, assuming that it is enough to put them where the
> speed limit deviates from the norm?

> My assumption - and I'm not a boating person so I may be wrong - is that if
> you're out on a boat with any working kind of navigation, you will know
> where the coastline is, and therefore you will automatically know where the
> 12nm boundary is - so having an explicit line would really only make sense
> where it deviates.

We have been discussing these issues in Italy and someone found the
treaty which contained a long list of points which are used to draw
the "baseline", the 12miles offset for the international waters is
calculated from this (in international treaties established) baseline,
not from the actual
coastline, so it doesn't matter how often we change our coastline: it
doesn't change the 12nm-water-border.

We were still discussing which reference system might have been used
in the treaty (if I recall right the treaty was before WGS84 was
invented) when user:Damouns imported a lot of these borders e.g. here:

with these tags:
admin_level = 2
border_type = territorial
boundary = administrative
maritime = yes
name = Territorial waters of Italy
ref = 118
source = EUROSION
source_ref = http://www.eea.europa.eu/data-and-maps/data/maritime-boundaries

so we stopped caring and started hoping (AFAIK, maybe someone checked
it) that this imported border was correct. At least it claimed to be
based on official data, which was enough for all of us ;-)

> I doubt that whoever put the current auto-generated boundaries in has
> actually checked whether these are overridden by any treaties.

Don't know for the German, Dutch or British borders, which have
already been sitting there for a while when "our" borders were
imported, but at least those later imported ones seem to be based on
official data. As stated above: when calculating them you should refer
to the "baseline" which is defined in treaties, using the actual
coastline would generally result in inaccurate data, even if it has
much more nodes ;-).


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