[talk-au] natural=land v natural=coastline

Jim Croft jim.croft at gmail.com
Tue Oct 6 14:37:31 BST 2009

For OSM purposes (as opposed to general mapping) the answer should not
be complicated.  If at high tide you drive into the water, you have
driven over a functional coast into the sea... :)

Of course, this won't work for mariners and lawyers... :)

My favourite estuary is the Fly River in PNG.  It just gets gradually
wider and wider and wider.  Somewhere the river becomes the ocean.
And there is no way to tell where it happens...


On Tue, Oct 6, 2009 at 11:35 PM, John Smith <deltafoxtrot256 at gmail.com> wrote:
> 2009/10/6 James Livingston <doctau at mac.com>:
>> On 06/10/2009, at 2:12 PM, John Smith wrote:
>>> Lake Eyre etc is so big they used natural=coastline... Although this
>>> comes back to the question the other day, where does the coastline
>>> start/end, legally speaking it cuts across bays, it doesn't go round
>>> them or up rivers...
>> I looked into this a while back and it's somewhat contentious. The
>> best I could figure out (which is quite possibly wrong) is that a
>> coastline ends and a river starts when there are no longer any tidal
>> significant effects. It's easiest to see if you have a slope, such as
>> a sandy beach. Consider the following, where at some point the high
>> and low tide levels get close enough to be negligable
> I realise this is potentially a very contensious issue.
> If you look at this from the point of view of territorial waters the
> coastline is from either the high or low tide marks, they spell it out
> in legalese and I can't remember off the top of my head, but the coast
> line cuts across any river/delta/bay mouths, except where the bay is
> partially inhabited by another country and then it's usually by
> seperate agreement.
> I honestly don't know which way is best to go here, since all
> definitions are reasonably subjective and would also depend on average
> tide conditions and so on and so forth.
> Another way we could look at this is to find out where salt and fresh
> water mix, but this too is probably tide and rainfall related.
> We also have the SRTM data which could be used to estimate elevation
> of water above mean sea levels, which would also depend on
> tide/rainfall at the time the STRM mission flew.
>> At the point where it changes from coastline to riverbank, you
>> obviously need to have the coastline run across the river, so as to
>> form closed shape. Whether you're supposed to have the riverbank do
>> the same to form a closed shape, I don't know.
> Actually it's the opposite, coastlines aren't really closed ways as
> there is no single coastline polygon or multipolygon, riverbanks on
> the other hand must be closed and must be either less than 2000 nodes
> or have a multipolygon relation.
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Jim Croft ~ jim.croft at gmail.com ~ +61-2-62509499 ~
... in pursuit of the meaning of leaf ...
... 'All is leaf' ('Alles ist Blatt') - Goethe

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