Talk:Proposed Features/Coastline-River transit placement

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Maybe the intended use of natural=coastline should be explained better.

  • It is right or does make sense to have a river (waterway=river + natural=water polygon) outside the coastline?
  • Must rivers have their end node in the natural=coastline?
  • How can the ocean polygons be obtained if the coastline is moved inside the river?
These are good questions which should probably be explained better on the wiki. Specifically:
  • Yes, the river line can and in practical mapping frequently is extended outside the coastline. This makes a lot of sense especially if there is a dug deepwater channel or a marked shipping lane. See for example [1].
  • There should always be a shared node but as said they can extend beyond.
  • Coastline polygons are available from [2], see also Coastline.
Ocean polygons are the same as coastline polygon? If yes, the Rio de la Plata case is clear and the coastline is where it sould be, in its exterior limit. If no, the question remains, How can the ocean polygons be obtained?
Yes, the only ocean polygon data in OSM are the coastlines so if you need an ocean polygon you use the processed coastline data. Subsections of the Ocean like marginal seas or bays are not currently mapped as polygons. --Imagico (talk) 17:46, 2 April 2014 (UTC)


In addition there is the matter of overlaps between the riverbank polygons and the coastline. These are rare but exist (like [3] and [4]) and there are no rules forbidding those. And overlap would underline the idea that some waterbody is both part of a river and the ocean. I did not specifically cover them in the proposal since that would further complicate things. My opinion is overlaps should be possible within the limits outlined in the draft.
--Imagico (talk) 08:12, 2 April 2014 (UTC)

The case of overlaping between River Elbe and the coastline, maybe is influenced by mapnik not showing the water polygons at low zoom, and probably we wouldn't be talking about this if mapnik rendered the Rio de la Plata water polygon at low zoom.

My opinion is overlaps between riverbank and coastline should be only when there are no clear limit between them. It's not the case of Rio de la Plata (max. wide 219 Km) , which exterior limit is clearly defined by IHO (International Hydrographic Organization [5].

Coastline refers to "marine environment". "marine" is defined as "related to sea or sea transport" [6] and "sea" is defined as "the salty water that covers a large part of the surface of the Earth, or a large area of salty water, smaller than an ocean, that is partly or completely surrounded by land" [7] The water of a river is not salty, so no "marine" and no "coastline"

First of all this is not primarily about the Rio de la Plata but about the consistency of mapping, the proposal is meant to establish guidelines so that rivers around the world are mapped in a consistent way. If the proposal is modified in a way that supports the current Rio de la Plata mapping that would be fine with me, this is however difficult to accomplish without changing a lot of other rivers around the world.
Concerning the limits of rivers in general and the Rio de la Plata in particular - the rules i drafted are oriented at what you describe as marine environment in some of its characteristics. Only if the river current is the dominating current in the water is the ocean water prevented from progressing 'upstream' and extending the marine environment. As can be seen in the literature, for example in [8] the outer part of the Rio de la Plata is clearly a fully marine environment. This can also be seen on satellite images like [9] where the brownish color or the river water ends near Montevideo. The IHO definition does not seem overly relevant here since it only defines the boundary of the Rio de la Plata as a sea and not as a river so it does not deal with the difficulty of separating river and ocean. --Imagico (talk) 17:46, 2 April 2014 (UTC)
The IHO document has the definition of the limits South Atlantic Ocean, (#32 page 18 and 19) and is explicit in that matter, the ocean ends where the river begins, and that limit is establiched in. Is a river, not a sea, "River of Silver" not "Sea of Silver"
Here [10] you have a clear definition of the estuary (from this article [11]
Here [12] you have a study of the plume of the river, including the salinity and some maps of the model.
The IHO document you cited documents the Limits of Oceans and Seas, not those of rivers. You might have noticed that the Rio de la Plata is the only river included there which - if anything - indicates the IHO considers it to be a marginal sea of the Atlantic Ocean. But this part of the discussion is getting very off-topic.

In "Rationale" you talk about different colours rendering to be a problem. In most of the aerial imagery of Rio de la Plata the waters of the river are clearly of another colour, not the same of the colour of the ocean. You talk that "will help avoid extreme cases like above", the Rio de la Plata case is extreme but is also real, so, IMO, there is no need to avoid it.

The more that I read, the most that I'm convinced that all this was to avoid a mapnik limitation, maybe the most old and extended case of Tagging_for_the_renderer

The opposite is the case - as i explained the standard map style is fairly immune against waterbody mapping inconsistencies since all waterbodies are shown in the same color, the only exception are the lowest zoom levels where only the coastline is displayed and therefore you can see this. Most other maps however (like [13], [14], [15], [16]) show ocean and rivers in different color, therefore the transit between river and ocean is always prominently visible and if this is not mapped consistently the map looks bad - but not because some flaw in rendering but because of inconsistencies in the data. Therefore i do not think this proposal is any more tagging for the renderer than any tagging convention in general which always have the primary purpose of ensuring some level of consistency in the data. --Imagico (talk) 17:46, 2 April 2014 (UTC)


The colour of the water in [17] is by the particles in suspension. This is fresh (salinity<0.05%) water. The oceans begins where the salinity is more than 3%, which is near Punta del Este in Uruguay and Punta Rasa in Argentina. This limit is obviously changing by the tidal or climatic conditions, but the scientifically and legally acepted limit is this. The influence of the great volume of fresh water in the ocean is more than most people expect. You should be watching salinity maps or models. Of course, you are also welcome to came here and personally taste the water, survey the zone, and enjoy the beaches. :-)

In wikipedia there are some global maps of salinity http://en.wikipedia.org/wiki/Salinity The detailed maps or models i found are in spanish. I can also link here if you like.

Please see the paper i have linked to at [18] which quite well documents how the water mixes in this case.
But I don't think it is productive to make this all about the Rio de la Plata - the question is if the proposed guidelines for placing the transit would be useful or not. As i have said before a salinity threshold like ocean begins where the salinity is more than 3% would not be a practically useful criterion since many bodies of water clearly belonging to the maritime domain (like Baltic Sea, Hudson Bay, Sea of Azov) feature a very low salinity and large rivers can reduce the salinity of the ocean far in front of the river mouth, especially if you only consider the surface layer.
If there are ideas for a better usable general criterion for placing the coastline i would be eager to hear.
--Imagico (talk) 23:37, 2 April 2014 (UTC)

This may be another interesting example to look at (Amazon and Anapu Rivers). To my non-expert eyes, the coastline extends pretty far upstream. http://overpass-turbo.eu/s/3M0

As far as i can see the coastline location at the Amazon is currently well within the limits of this proposal. Also in global comparison this is a fairly moderate placement. The Amazon is somewhat special due to its very high water throughput which would in theory allow moving the coastline quite a bit out into the ocean under the rules described here, further than it would make sense from a cartographic viewpoint, but this is a singular case and not enough reason to be more restrictive in general IMO. --Imagico (talk) 13:53, 19 June 2014 (UTC)

Bilder

Ein paar illustrierende Bilder wären hilfreich. Gruss, --Markus (talk) 20:04, 12 September 2014 (UTC)