Message: 3
Date: Wed, 5 Sep 2018 18:03:36 +0200
From: Christoph Hormann <o...@imagico.de>
To: "Tag discussion, strategy and related tools"
<tagging@openstreetmap.org>
Subject: Re: [Tagging] Coastline for rivers, estuaries and mangroves?
Message-ID: <201809051803.36467....@imagico.de>
Content-Type: text/plain; charset="utf-8"
On Wednesday 05 September 2018, Joseph Eisenberg wrote:
> Specific examples:
>
> 1) This changeset on the River Dart in southwest England was the
> source of the Help site question:
> https://www.openstreetmap.org/changeset/61959067
The coastline closure there:
https://www.openstreetmap.org/way/216482240
is both below the lower limit of the proposal and below the the range
i
can imagine a meaningful coastline closure rule to allow.
I would however be interested in hearing any universal rule that would
allow this kind of placement based on physically observable criteria
and that would maintain the coastline as a meaningful geometry on its
own.
> It looks like quite a large estuary, much wider than the non-tidal
> part of the river upstream.
That is largely not really an estuary but more of a ria. I have no
data
for this at hand but you can likely see an abrupt change in the
elevation profile near Totnes where the submerged section of the
former
river valley starts. So in this case it would make a lot of sense to
place the coastline closure near the upper end of the tidal section
because this is much better defined in terms of physical geography.
> 2) The estuaries and mangrove tidal channels in this area:
> https://www.openstreetmap.org/#map=11/-4.8806/136.9339
Here i likewise see no meaningful motivation for the current coastline
placement - like here:
https://www.openstreetmap.org/way/614052686
Poor image quality in the available sources makes identifying the
limit
of the mangroves difficult, you really need to make use of available
lower resolution open data images in the area for proper maiing here.
But you can conclude a few thing from the structure of the network of
channels. For example
https://www.openstreetmap.org/relation/7301266
is quite clearly not a river but a tidal channel (there is no river
feeding it, it is just draining seawater that has entered during
raising tide).
> I previously changed the coastline to be closer to the river mouths
> in another section of coast to the southeast, but perhaps I should
> change it back? The whole idea of coastline around mangrove swamps
is
> most confusing. I don't think the mangroves should be outside of the
> coastline, but where then should it be?
Common practice is to place the coastline at the outer end of the
mangrove forest. This is a pragmatic solution because placing it
inside the mangrove would be non-verifiable. Of course mapping the
mangrove is important for the data to be meaningful in this case.
--
Christoph Hormann
http://www.imagico.de/
