Proposal:Rio de la Plata

Rio de la Plata
Proposal status:	Rejected (inactive)
Proposed by:	Kanpaidaisuki
Tagging:	see the "Proposed Tagging" section.
Draft started:	2025-08-02
RFC start:	2025-09-26 [RFC Proposal Rio de la Plata]
Vote start:	2025-10-15 00:00:00 (UTC)
Vote end:	2025-10-28 23:59:59 (UTC)

Introduction to natural=coastline : Three rules that do not work separately; they have a hierarchy, starting with the first as the highest.

This text is just an introductory summary; it does not define or propose any changes to the natural=coastline tag. If you want to change anything about coastline, please create the proper proposal presenting the change.

• This proposal does not propose any changes within natural=coastline tag.

• This proposal does not propose any changes within the natural=coastline definition.

Rule 1: Continuous Way

Although its definition states it should be used for maritime coastlines, and it is often presented as a “complex” tag, natural=coastline is actually simple to explain if you start from the basics: This tag is primarily and exclusively used to delimit land from water. Everything you see mapped on OSM sits inside a polygon defined by a “natural=coastline” way that encloses it all.

For this reason, there is a fundamental rule: this way should never be discontinuous.

A coastline way that encloses an area to establish the land boundary. (There are no water-with-water boundaries in this example.)

Problem:

• In reality, coastlines are not continuous: there are rivers, mangroves, deltas, etc. that are not strictly “coastline”.

A coastline way, discontinuous.

• But because this would leave the coastline broken, mappers typically choose one of two approaches — ignoring the literal wiki definition but respecting the main purpose: to keep the coastline continuous.

Rule 2: Mapper’s Criterion

Note: This example only shows two of the many possible elements that could be considered; however, all the elements accounted for are ultimately reduced to just two options.

Option 1	Option 2
Image 3: coastline drawn outside the polygons	Image 4: coastline drawn inside the polygons

On OSM you will find natural=coastline mapped using either approach, bending its definition and letting each mapper draw the coastline wherever they personally feel it should go.

Rule 3: A Defined but Undefined Limit — The Coastline Paradox

• You are invited to read about the Coastline paradox .

The 19 January 2021 edit added — without vote or community backing — the following statement:

“Bays and other large tidal salt-water areas are part of the sea if they are connected to the sea and should always be tagged as such.”

This wording is problematic. Starting with the word “large” — it’s not a unit of measure. This collapses into the Coastline paradox since OSM uses a vector system, boundary criteria should be considered independently of size.

Bringing “salinity” into the definition of “coastline” is another absurdity. “Salt-water” is not a unit of measure either. At what concentration of dissolved minerals does water become “ocean”? What do we do with salty rivers? Let’s examine:

Diffuse Salinity	Effect of Rainfall
A river with multiple salinity zones. Defining a coastline based on “percentage of salinity” would require scientific studies. Defined method: salinity Method actually used: Rule 2.	Rainfall lowers salinity to nearly zero, even if the river itself receives salty inflows. Should rainfall frequency set the real coastline boundary?

Introduction to renders

This text and graphic state that renderers are external activities to the OSM databases. The servers of these tools that provide tiles or vectors depend on developers (proprietary or not) who apply judgment over their code, which is 'external' to the wiki. What is being made explicit is that incorrect tags or data should not be used so that these tiles, for example, can display data at high zoom levels.

• does not propose any changes to third-party access to or use of OSM data.

how it works:

If the client or the server owner of the renderer doesn’t like how the map tiles are rendered, they need to update their code, because on OSM we Don't map for the renderer

• Does this proposal have anything to do with the renders?
  • The answer is no.
• So, is it necessary to consider them?
  • The answer is no.

Introduction to sea

• sea:

ocean,sea,océano,mar,océan,mer,oceano,mare,oceà,ozean,meer,oceaan,zee,hav,osean,úthaf,haf,океан (okeán),море (more),ωκεανός (okeanós) θάλασσα (thálassa)okyanusdeniz محيط (muḥīṭ) بحر (baḥr) אוקיינוס (okyanos) ים (yam) 海洋 (hǎiyáng) 海 (hǎi) 大洋 (dàyáng) 海洋 (kaiyō) 海 (umi) 大洋 (taiyō) 해양 (haeyang) 바다 (bada) महासागर (mahāsāgar) समुद्र (samudra) सागर (sāgara) bahari bahari kuu

• not sea:

river, lagoon, estuary, pool, rivière, fleuve, lagune, estuaire, mare, bassin, fiume, estuario, pozza, stagno, rio, lagoa, poça, riu, llacuna, estuari, bassa, Fluss, Lagune, Ästuar, Pfütze, Tümpel, rivier, poel, elv, flod, estuarie, pyt, älv, lagun, estuarium, pöl, á, lagúna, óshólmar, pollur, река, лагуна, эстуарий, пруд, лужа, ποταμός, λιμνοθάλασσα, εκβολή, λιμνούλα, nehir, ırmak, haliç, gölcük, نهر, بحيرة, مصب النهر, بركة, נהר, לגונה, שפך, פי הנהר, שלולית, 河, 江, 泻湖, 河口, 池塘, 水坑, 川, 潟湖, 河口, 池, 水たまり, 강, 석호, 하구, 연못, 웅덩이, नदी, लैगून, मुहाना, पोखर

Because there are many words to say the same thing, keep in mind that this proposal is meant to be read and built within your mind as to what is being proposed. An AI will summarize this proposal, but the AI does not know what is actually being proposed.

Proposal

This proposal is to reclassify the Río de la Plata (relation 3474227) and its constituent waters to be tagged as natural=water and water=river, replacing the current natural=coastline tag for its banks. This change aims to align the OpenStreetMap data with the geographical, hydrological, and legal reality of this major water body.

• maritime=yes tag is deleted.
• is_in:ocean=Atlantic Ocean tag is deleted.

natural=coastline will be applied to a single way (since nowhere in the proposal do we state that rule No. 1 should be broken) with the relation 3474227 but not necessarily in a possible future, because the coastline shifts over time (erosion, etc.)., which will be up to the community.

Situation Summary

• Current (De Facto) Situation: The Río de la Plata is treated as an inlet of the Atlantic Ocean, with its banks tagged as natural=coastline. This practice, while established, is primarily based on its large-scale appearance and marine influence, not its predominant physical characteristics.
• Proposed Situation: Recognize the Río de la Plata for what it is: the final, estuarine stretch of one of the world's largest hydrographic basins. This involves treating its perimeter as a riverbank (natural=water, water=river) rather than an oceanic coast.

Relation 3474227

Current (De Facto) Situation:	Proposed Situation:
Currently (rule2), natural=coastline is being used to separate water from water.	Also (rule2) natural=coastline is being used to separate water from water.

Rationale

The current natural=coastline tagging is a simplification that fails to accurately represent the complex nature of the Río de la Plata. Scientific evidence and international treaties define it as a river with an estuarine regime.

1. Geographic and Scientific Rationale

• It is a river in an estuary, not a sea: The Río de la Plata is the terminus of the second-largest basin in South America, formed by the Paraná and Uruguay rivers. It discharges an average of 20,000 m³/s of fresh water into the Atlantic. The scientific paper "Physical oceanography of the Río de la Plata estuary" (Guerrero, 1994) explicitly defines the area as a distinct estuarine system, characterized by the interaction between massive continental discharge and the adjacent sea.

Río de la Plata Basin	Río de la Plata Basin flow
It discharges an average of 20,000 m³/s of fresh water into the Atlantic.	the same image, but with arrows, to understand the reason for its freshwater flow, and why the ocean does not play a role. visit this news piece featuring storms in the region.

• Salinity and Tides define a River-Dominated Estuary:
  • Salinity: The system has a scientifically documented two-layer structure. The Guerrero study describes it as a "typical two-layer stratification: a dilute, less dense surface layer of continental origin, over a saline, denser bottom layer of platform origin." This means the dominant surface is fresh river water. The penetration of the saline bottom layer (the "salt wedge") is limited by topography, confirming that it is an intrusion into a river system, not a saline sea in its own right.
  • Tides and Wind: The astronomical tidal amplitude is very low (0.2 to 0.5 meters in Buenos Aires), a negligible value compared to oceanic tides (typically 1 to 4 meters). The same study highlights that dominant winds are a primary driver for surface water discharge, often having more impact than the weak tidal signal on large-scale water movement. This is characteristic of a large, shallow, river-dominated water body.

• Depth and Morphology: The river is extremely wide but very shallow. Its natural depth rarely exceeds 5-10 meters outside of dredged channels. This necessitates constant dredging to allow for deep-draft navigation, an activity typical of navigable rivers, not open sea coasts.

Canal de Acceso| dredged channels

Canal de Acceso| dredged channels

2. Legal and International Rationale

• Treaty of the Río de la Plata and its Maritime Front (1973): Argentina and Uruguay signed a treaty that clearly defines the river's limits. Article 1 establishes its outer boundary as the imaginary line connecting Punta del Este (Uruguay) with Punta Rasa (Argentina). Inward from this line, the body of water is legally the "Río de la Plata"; outward, it is the "Maritime Front." Our tagging should respect this binational, legal definition.

3. OpenStreetMap Principles

• Don't map for the renderer: The use of natural=coastline appears largely motivated by the desire for renderers to display the area with the color of the ocean. This is an incorrect approach. OSM's priority is to map the reality "on the ground" (verifiability), and the reality is that this is a river.
• Data Accuracy: Classifying the Río de la Plata as a coastline introduces errors in data analysis, such as hydrographic basin calculations, river network studies, and environmental modeling applications.

4. Addressing Counterarguments

• "It's salt water and has tides": As demonstrated above, its surface is predominantly fresh water, and the underlying saline layer is an intrusion. Its water dynamics are more influenced by wind and fluvial discharge than by oceanic tides.
• "The name 'Río' (River) is just a name": It is a precise geographical designation, supported by its hydrology (freshwater flow, two-layer stratification, shallow depth) and legal status.
• "Changing this will break global coastline update scripts": This is a technical challenge, not a geographical argument. Data accuracy must take precedence over the technical limitations of downstream tools. The solution is to adapt the scripts to correct data, not to maintain incorrect data for the sake of the scripts.

Proposed Tagging

It is proposed that the ways currently forming the perimeter of relation 3474227 and tagged as natural=coastline be modified.

1. For the relation (3474227):

• It should be tagged type=multipolygon, natural=water, and water=river.
• maritime=yes tag is deleted.
• is_in:ocean=Atlantic Ocean tag is deleted.

2. For the ways forming its perimeter:

• The ways representing the banks (currently natural=coastline) should be part of the multipolygon relation with the role `outer`.
• These ways would no longer need the natural=coastline tag, as their inclusion in a natural=water relation defines their nature.

3. Rule No.1 of natural=coastline

• If the proposal is approved, natural=coastline will be applied to a single way (since nowhere in the proposal do we state that rule No. 1 should be broken) with the relation 3474227 but not necessarily in a possible future, because the coastline shifts over time (erosion, etc.)., which will be up to the community.

/*
  This query finds all ways that are members of the
  Río de la Plata relation (3474227) and are also
  tagged as natural=coastline.
*/
rel(3474227);
way(r)[natural=coastline];
out geom;

External discussions

• A Data Working Group (DWG) representative noted the need for community consensus before large-scale edits are made.
• Community forum discussion on the topic.

See Also

• Oceanografía física del estuario del Río de la Plata y el sistema costero de El Rincón. Noviembre, 1994 (Physical oceanography of the Río de la Plata estuary...)
• Treaty of the Río de la Plata and its Maritime Front (1973)
• Hasta cuando continuaran las lluvias en argentina (beautiful images, in which I highlight the importance of storms)

Comments

Please comment on the RFC Rio de la Plata.

Voting

Voting closed

Voting on this proposal has been closed.

It was rejected with 1 vote for, 16 votes against and 1 abstention.

Proposal fails as it did not achieve the 75% approval threshold.

• I oppose this proposal. The current tagging is fine and is consistent with other large estuaries. This proposal has demonstrated no way in which any data consumer is harmed by the current tagging. I do not think any of the scientific or legal arguments are relevant here. It's a large body of water, at sea level, connected to the ocean, therefore should be outside of the `natural=coastline` ways. It's fine to have a natural=water + water=river polygon outside the coastline, like the present tagging. --ZeLonewolf (talk) 11:45, 15 October 2025 (UTC)
• I approve this proposal. This tagging needs to be corrected to accurately represent the river, both geographically and legally. The proposal is simple and well-documented. —Preceding unsigned comment added by AndresDuhour (talk • contribs) 11:57, 15 October 2025 (UTC)
• I oppose this proposal. Same as ZeLonewolf. This proposal is inconsistent with how tidal estuaries are tagged worldwide. No arguments presented here persuaded me that the Rio de la Plata is unique in any significant way from other places and merits going against worldwide consensus. Many parts of the ocean and other estuaries are shallow and yet mapped outside of the coastline, and treaties are not binding to OSM tagging, for two examples --Willkmis (talk) 12:26, 15 October 2025 (UTC)
• I oppose this proposal. I suggest people read the request for comments that has many not-included suggestions, to see why this proposal should be rejected --Gedankenstuecke (talk) 12:29, 15 October 2025 (UTC)
• I oppose this proposal. This proposal indicates that it will move the natural=coastline tag to a way that is too far "downstream" to be reasonable. The coastline is normally tagged at or near the high water mark when bordering land or when the river dominates the flow for river mouths. Contrary to the description of the tidal range above (0.2-0.6m), websites reporting tides indicate that on the 4th of November the tidal range in Buenos Aires will be 1.08m, not unusually small, despite it being approximately 200km "inland" of the new proposed land sea border. There are also indications that sediment is being transported "upstream" along the shoreline by longshore drift (often regarded as a coastal process) rather than being pulled "downstream" by the river indicating that the river is not the overriding factor in those areas. Finally even on the topic of salinity, studies (e.g. this one) show that the water only remains 'fresh' as far as Montevideo and even then only at low-medium tide (~80 km inland from the proposed coastline). Given that discussion of this proposal has been banned on the community forum this vote is also likely to be invalid on procedural grounds as an announcement of the vote has to be made there according to the current proposal process. --InsertUser (talk) 13:02, 15 October 2025 (UTC)

  As I’ve already told you several times, if you had the decency to read what both publications actually say, you’d find that they contradict what you’re claiming. The first one shows the predominance of the inflow’s activity and the effect of the winds | the tide rises by 1.08m due to wind action | and the second one, “SALINITY SIMULATIONS OF THE RIO DE LA PLATA”, shows in FIG3 that salinity is close to 0 at times because of the inflow, but it never reaches oceanic levels. If it’s an estuary, have the decency not to treat it as an ocean. The forum was what it was: it had very little to do with the proposal.--Kanpaidaisuki (talk) 16:59, 15 October 2025 (UTC)

• I oppose this proposal. Same as InsertUser. In principle I'm open to changing the location of the coastline, but failure of the proposal author to constructively engage the community left a very bad taste. It seems that linguistically and culturally the Rio de la Plata is called a "river" and so the proposal author adamantly wants to align the coastline tagging with those linguistic and cultural norms at the exclusion of all other considerations. --Adamfranco (talk) 13:48, 15 October 2025 (UTC)
• I have comments but abstain from voting on this proposal. This proposal tries to use the proposal system (which is otherwise used to develop general mapping and tagging ideas and principles) to codify an individual local mapping decision and at the same time deliberately does not in any way formulate general mapping and tagging principles. No matter if the proposal is accepted or rejected it would imply the results stand above the sovereignty of the local community in making mapping decisions and this way would put into question the primacy of the local community as the very foundation of OpenStreetMap. Therefore i am neither for nor against this but object to the very idea of using the proposal system this way. The results of this vote should have no bearing on how the geography the proposal discusses is going to be mapped in OSM because that decisions is the prerogative of the local community. --Imagico (talk) 16:42, 15 October 2025 (UTC)

• I oppose this proposal. OpenStreetMap is not a place for alternative truth. Please try https://opengeofiction.net instead. --Nospam2005 (talk) 17:23, 15 October 2025 (UTC)
• I oppose this proposal. Although a strict MHWS mapping of the coastline is frequently inappropriate for tidal rivers, putting the mapped coastline far upstream from the generally-understood coastline, this proposed mapping of Rio de la Plata moves the mapped coastline too far in the other direction. --Carnildo (talk) 18:03, 15 October 2025 (UTC)
• I oppose this proposal. For all the reasons outlined by others above. Voting should never have been opened at all, because the forum discussion has been closed due to repeated etiquette violations by the proposer. --clay_c (talk) 18:46, 15 October 2025 (UTC)
• I would like to express a degree of incredulity at this proposal. 'nuff said Ezekielf (talk) 19:41, 15 October 2025 (UTC)
• I oppose this proposal. Whilst I can understand the desire to be able to tag, and from that map, that the Rio de la Plata is a very different environment both to the rivers that feed it and to the South Atlantic into which it itself feeds, this ill-thought-out and ill-argued proposal is not it. I'm sure that many people would be open to the definition of (something) that reflects a transition between estuary and ocean, and might even support codifying the more pragmatic definition of `natural=coastline` some way downstream of MHWS that is used on many tidal rivers. However, the consistent torrent of abuse in the forum from the proposer Kanpaidaisuki (in place of any reasoned argument) ruled out any possible compromise. Imagico is entirely correct that this "deliberately does not in any way formulate general mapping and tagging principles" (and for that reason this also makes no sense as a proposal). Ezekielf's analysis is also entirely correct. SomeoneElse (talk) 19:58, 15 October 2025 (UTC)
• I oppose this proposal. For all the reasons outlined by others above. --Vincentius (talk) 12:33, 19 October 2025 (UTC)
• I oppose this proposal. For the same reasons given above. It should also be noted that these boundaries are published by the Uruguayan government and, as such, their design in OSM should be independent of decisions made by mappers or communities. The actual tagging is appropriate. Also, as already argued, the design of estuaries or other natural features, such as mangroves, is not impeded by the existence of a coastline. Although there are criteria for its delimitation in the environment, the coastline is imaginary and represents a boundary for the land-sea domains interface. Giving more elements, considering only the Uruguay side, please, visit this link: https://www.ambiente.gub.uy/oan/documentos/Nota_Calculo_Inicial_Lineas_De_Costa.pdf and also this: https://www.ambiente.gub.uy/visualizador/index.php?vis=sig - layer NAP Costas and Línea de costa percentil 80 --Raqueldeziderio (talk) 03:54, 20 October 2025 (UTC)<nowiki>

  "OSM should be independent of decisions made by mappers or communities." That's what you have to tell to DWG, but thanks for your attempt at "no data needed", but you still offer it.--Kanpaidaisuki (talk) 00:30, 23 October 2025 (UTC)

• I oppose this proposal. The current tagging is OK and according to the rules, not matter to change this. This discussion now leads back several years, the result is always the same: NO --Kech61 (talk) 06:55, 20 October 2025 (UTC)
• I oppose this proposal. I haven't looked into the tagging change proposed and have only tangentially followed the discussion, but your apparent lack of openness to discourse makes this an immediate non-starter. I am confident that you have valid reasons in favor of this tagging change, but it is not possible for this proposal to get anywhere unless you engage in discussion with your community of fellow mappers. It is not appropriate to waste community members' time by persistently refusing to engage in kind, respectful, productive discourse. When you are willing and ready, we would be happy to discuss, though such a movement would likely be best discussed in a separate proposal. --Pwbriggs (talk) 04:33, 22 October 2025 (UTC)
• I oppose this proposal. no special case for one single case --Cquest (talk) 13:39, 28 October 2025 (UTC)
• I oppose this proposal. For all the reasons outlined by others above. --Bandino (talk) 17:28, 28 October 2025 (UTC)

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Votes after 2025-10-28 23:59:59 (UTC) - end of voting period

---

• I have comments but abstain from voting on this proposal. I agree it would be good to eliminate the simultaneous duplicate definition of the same water body via both natural=water and natural=coastline (which unnecessarily forces renderers to draw the same area twice), but other solutions may be better here, given the enormous width of this . Consider the possibility of keeping the area on the sea side of the natural=coastline, but changing natural=water into e.g. natural=bay or some dedicated new tag for large estuaries. Beware there are some renderers that draw natural=coastline and natural=water in different shades of blue, consider what is a desirable outcome for such renderers. --JeroenvanderGun (talk) 17:36, 29 October 2025 (UTC)