Author Archive

Mapping Internal Administrative Boundaries (part 1)

December 2, 2019
Kevin Danaher

Several weeks ago, Marissa and I attended an event at Columbia University’s Lamont-Doherty Earth Observatory on mapping internal administrative boundaries. The purpose of this conference was to bring together professionals from the public and private sectors and from all different backgrounds (GIS, human geography, cartography, etc) to have a discussion about the practices and problems of mapping internal boundaries. There are a variety of freely available data sources for boundaries, such as GADM and Natural Earth, however there are also a multitude of commercial providers who maintain and license their own internal boundary data. And depending on how the data is being used, one of these options might be better than the other, but it is not always a straight forward process to make this decision.

Although our primary focus here at International Mapping has been on international boundaries (often referred to as “admin 0” or “ADM0”) and disputes, there are obvious overlaps in dealing with the sub-national boundaries nested hierarchically within national boundaries. We very often wrestle with internal boundaries when making maps for our clients, trying to ensure the data is up to date not only in the geometry/shape of each administrative unit, but also in the naming and attribution.

In this post I hope to summarize some takeaways from the event as well as some of the primary difficulties we face when mapping and maintaining admin boundary data. I refer to this post as part 1 because in an upcoming post I will go over some ideas for moving forward.


To kick off the event, we heard from a panel of several speakers about their use cases and challenges with internal boundaries, and on the importance of mapping sub-national administrative units. One longer term effort has been led by the UN with its Second Administrative Level Boundaries (SALB) project, which was launched in 2001. In short, the goal of SALB is to aggregate internal boundary data directly from UN members states, collected from authoritative sources such as individual National Mapping Agency or relevant divisions of government. Nearly two decades later, the project’s goal has not fully come to fruition, primarily due to a lack of participation from member states. At the time of this writing, the SALB site lists datasets contributed by only 45 of the 197 states listed.

“Current status” map of SALB

The event also featured a number of lightning talks from professionals in both the public and private sector, discussing their interaction with internal boundaries or showcasing products they’ve built around them. It was quite insightful to hear common (and familiar) threads on the difficulties so many are facing when dealing with boundary data.

Difficulties in Mapping and Maintaining Administrative Boundary Datasets

The list below comes from way too many hours spent dealing with administrative boundary data, but as mentioned above these frustrations are shared by many:

  • Finding “authoritative” data

    In some cases, internal boundary data is distributed by countries via the web and maintained by some designated agency. In these rare cases we would consider the data authoritative, as who else but a country themselves can decide on their internal organization? However more often than not data isn’t available in this way, and it is difficult to tell whether data from other sources can be considered reliable, well-sourced and/or up to date.

    Sometimes, a list of administrative units might only be found in a primary source or authoritative piece of legislation. However with no spatial data or map accompanying the legislation, how are we to handle these instances? I recently found this to be the case while attempting to update Mali’s cercles (ADM2 divisions). A set of 2012 decrees established a number of new ADM1 regions and defined the cercles making up each. After some time spent researching, I came to discover that the legislation was way ahead of the reality on the ground, and that we likely won’t see the newer divisions come to fruition for years to come.
  • Licensing, permissions, copyright and use restrictions

    Associated permissions, licenses or use cases attached to a data source can restrict a user from any commercial use, or the modifying and combining of data with other sources. This often leads to datasets being updated and utilized on an internal basis, and not shared back to the broader community for fear of violating permitted uses. In many cases permitted use can also be vague or confusing, with even the “authoritative” datasets mentioned above having tight restrictions on use.
  • Assigning of codes or unique identifiers

    Internal administrative units are often used for mapping tabular or statistical data by creating choropleth or other maps for data visualization. A major component of this is tracking unique identifiers for each unit in order to join the tabular data to the spatial. There are a number of methodologies and standards for these unique identifiers, and it is up for debate which is best, however it is often likely that the datasets you download will require some additions or “QC” to ensure an accurate join to your spatial data.
  • Resolution or intended scale for data

    This is how detailed the data is. We describe Sovereign Limits resolution as holding up at scales of 1:25,000 and larger. More often, Sovereign Limits boundaries have been created at even larger scales than this. For admin units that we source, the resolution of data will rarely hold to those standards. We have learned to expect huge variation when it comes to resolution in administrative data from different sources. It will always be ideal to locate and make use of the highest resolution and up to date data available.
  • Maintaining topology

    This is the “connectivity” of the spatial data. Unintended gaps or overlaps between admin unit data can be seen as problematic, as this type of data is intended to align like puzzle pieces. So, a certain amount of processing and data validation is often required to make sure the topology is sound. While nice and tidy topology isn’t required in spatial datasets, it is often a sign of a sloppy data quality when polygons crisscross one another or aren’t aligned seamlessly. Editing or processing data can introduce its own errors, so it is often a time consuming task to ensure that the topology is sound.
  • Coastline

    Coastline data comes in various resolutions, and in many cases can be quite cumbersome to deal with. Admin unit data sourced for coastal states will nearly always include a coastline in the dataset, and the coastline for one country dataset is extremely unlikely to match the source or resolution used in the coast of another. This means that, for a cohesive dataset, it is necessary to process admin unit data to either 1) a single coastline source or 2) to ignore coastline and extend admin units to the edge of a territorial sea, avoiding the difficult task of maintaining complex and cumbersome coastline data.
  • Disputed areas

    The way one views the world’s boundaries will have an effect on the treatment of administrative units in many places. For example, if I am creating a map of Georgia (the country), should municipalities within the breakaway republics of Abkhazia or South Ossetia be included? Most often the answer depends on your or your organization/client’s geopolitical views, adding a further complexity in dealing with this data.

There are plenty of other fun issues that come up when dealing with this data, but I believe the above are the most common and pertinent. As said earlier, in a future post I’ll plan to share some thoughts for strategies moving forward, but in the meantime I need to check into the status of Mali’s cercles again.

A Drone Shooting, Maritime Sovereignty and Airspace

June 28, 2019
Kevin Danaher

With the recent downing of a US drone by Iran, the most pertinent question at this point is: “Where was the drone when it was shot down?” With accurate coordinates, we can easily verify whether it had strayed into Iranian-controlled, national airspace, or if it remained beyond in international airspace.

However, accurate coordinates are more difficult to come by when dealing with 3-dimensional space, and both the Government of Iran and the Government of the US have supplied a different set of coordinates as to the location of the drone before it was shot down. Rather than getting lost in the weeds over where the event took place, in this post we want to briefly discuss the customary international laws defining sovereignty limits on the earth’s surface and above it, namely UNCLOS-III, and the zones of jurisdiction it defines.

National v. International Airspace

Simply put, airspace is divided into two categories, “national” and “international.” These classifications are based on whether the surface of the earth directly below is part of the sovereign territory of a recognized independent state, or not:

National airspace corresponds with that out to the edge of the territorial sea of a state, including archipelagic waters, internal waters, and the land itself. Under the Law of the Sea, a coastal state can claim up to a 12 nautical mile territorial sea from its baselines (either the low tide coast or simplified, straight-line segments declared as “straight” or “archipelagic” baselines). Out to the edge of the territorial sea, a state has “full” sovereignty and jurisdiction equivalent to that on its land. For an unrelated, interesting exercise I did on territorial sea limits, check out this post.

Zones of maritime jurisdiction, overlaid on a Sentinel-2 image captured June 23, 2019

International airspace is that beyond the territorial sea, corresponding to a state’s contiguous zone, exclusive economic zone, and outward into the high seas. The contiguous zone is the maritime space between 12 and 24 nautical miles from a state’s baselines, where they can exercise some authority relating to wrongful activity committed within their territorial sea. The exclusive economic zone (EEZ) is the space between 12 and 200 nautical miles from the baselines, where a state has some extended sovereignty for economic purposes (fishing, oil exploration, etc). The high seas are areas beyond the 200 nautical mile EEZ.

Where was the Drone?

A coordinate about 4 nautical miles inside the Iranian territorial sea limit was supplied by Iranian officials, while the United States submits an entirely different location, closer to the center of the Strait of Hormuz and beyond any state’s territorial waters. Without clarity on the true coordinate and the path of the drone it is difficult to draw any clear conclusions, but the drone was either within Iran’s national airspace as they claim, or not.

In any case, if either of the locations supplied are even remotely accurate, the drone would’ve been downed in either the Iranian territorial sea or EEZ, or in the EEZ of Oman (in this vicinity it also would’ve been in the contiguous zone of either state as well, however this is likely irrelevant). As discussed above, none of these are classified as international waters, but the airspace over the EEZ would be considered international airspace.

Bonus: Attempts to Verify the Location

With the right satellite image captured at the right time, it would be possible to gather some evidence to independently verify the location this incident took place. As civilians, we don’t have ready access to high resolution, “on-demand” satellite imagery, however we often look to open satellite data sources such as the European Space Agency’s Sentinel or Landsat to derive data or make temporal observations.

Reports indicate that the drone was downed June 19th at 23:35 UTC. A search of Sentinel imagery shows a capture available in the vicinity on the 20th at 06:52:28 UTC. Unfortunately for us, though, the image does not quite extend to our area of interest.

A search of Sentinel imagery from Sentinel-Hub EO Browser yields no captures in the vicinity we need. Drats.

If we could find an image in close proximity to the alleged time of the incident, we might look for increased maritime activity in a particular location or a debris field from the downed drone. However Sentinel imagery captured June 23rd shows no signs of either. It is also likely commercial satellites would have captured something, so we might keep our eyes out for imagery from this time period as it becomes available. In the meantime, though, we’ll just keep following the developing story surrounding this incident.

The Situation at Mouchoir Bank

February 28, 2019
Kevin Danaher

In the Caribbean, there is a little-known area of contention between the United Kingdom and Dominican Republic, and it hinges primarily on a single seamount called Mouchoir Bank. This post goes over the recent history of this section of the Caribbean, and the events that have brought us to this review of the current status of Mouchoir Bank.

A Brief History

On 2 August 1996, the Dominican Republic and United Kingdom signed an agreement delimiting the maritime space between the British Overseas Territory of Turks and Caicos and the Dominican Republic. The maritime boundary they established followed a path of simplified equidistance between mainland Dominican Republic and Turks and Caicos Islands. Based on the course of the boundary defined in this agreement, several seamounts were divided between either State’s Exclusive Economic Zone (EEZ). These are Mouchoir Bank, which fell on the Turks and Caicos side of the boundary, and Silver and Navidad Banks on the Dominican Republic side. To date, however, the Agreement has not been ratified by either party and is therefore not in force.

On 22 May 2007, the Dominican Republic released Act 66-07, which repealed and replaced all prior legislation regarding declarations on maritime space (Act Nos. 186 and 573). Most notably, Act 66-07 declared Dominican Republic’s archipelagic status, defined turning points for an archipelagic baseline, declared internal waters and historic bay closings, and listed 498 coordinates defining the outer limits of an EEZ. The archipelagic baseline and EEZ defined in Act 66-07 overlapped and extended beyond the 1996 boundary Agreement with the United Kingdom.

The unratified maritime boundary Agreement between the Dominican Republic and the United Kingdom is shown above, along with an equidistance scenario utilizing Dominican Republic’s claimed base points to the north and a strict equidistance scenario to the south. At this point in time, the Dominican Republic has not settled any maritime boundaries with Haiti or its neighbors to the north or east.

Five months later, the United Kingdom and the United States submitted a joint demarche to the United Nations opposing the Dominican Republic’s legislation. Specifically, the two governments did not accept the Dominican Republic’s claim of archipelagic status, nor the legitimacy of the turning points defining their archipelagic baselines. Further, both States rejected the EEZ, internal waters and historic bay closings defined in Act 66-07.

Mouchoir Bank

Although not stated directly by the parties involved, in contention is the furthest west of the seamounts on which the Dominican Republic lays claim, Mouchoir Bank. In Article 8 of Act 66-07, Dominican Republic places several base points along the feature for defining their archipelagic baseline. Additionally, Mouchoir Bank is west of the 1996 maritime boundary agreed between United Kingdom and Dominican Republic, which placed it in Turks and Caicos’ EEZ. Although that maritime boundary agreement has not been ratified, it is clear that there is a discrepancy over the status and sovereignty of the feature, especially given the United Kingdom’s dissent to the claims of Dominican Republic’s Act 66-07, as expressed in their communication to the United Nations on October 18, 2007.

Sentinel imagery shows the shape of the seamount, as well as several features breaking water. The archipelagic baseline claimed by Dominican Republic is shown, as well as several points that form the baseline. Plotted as provided in Act 66-07, these archipelagic base point coordinates do not appear very accurate at large scale. However, the legislation does note that the plotting “shall be adjusted to the corresponding values subject to in situ verification by the Dominican State.” Archipelagic base points 4 through 6 are intended to be connected following the low-tide elevation of Mouchoir Bank.

Upon review of satellite imagery, it appears that there is at least one feature of the Bank consistently above water, however it is unclear based on this image capture whether any other parts of the Bank are above water at low tide, as the Dominican Republic suggests in their construction of the archipelagic baseline using base points 4 through 6, continuing “… at low tide to the following point” along the bank.

Dominican Republic’s Maritime Claims

Dominican Republic’s Act 66-07 of 22 May 2007 defined the outer limit of an EEZ as well as turning points for an archipelagic baseline encompassing Mouchoir, Silver and Navidad Banks. Of note, the outer limit is 200 M from their claimed archipelagic baseline, and gives full weight to Navidad Bank in an equidistance boundary with Puerto Rico (Isla de Mona and Isla Monito are ignored in this equidistance calculation, but a 12 M limit from these Puerto Rican features is respected).

Claims set forth in Act 66-07 are shown above, including the extent of the Dominican Republic EEZ claim, archipelagic waters, and historic bays.

Equidistance Scenarios

Taking away past agreements and legislation instated by Dominican Republic or United Kingdom, we can assess how various scenarios could play out using natural features and the configuration of the states’ coastlines.

Below are two equidistance scenarios, illustrating how the path of a boundary could change should the seamounts be ignored or counted.

Allowing Mouchoir Bank full weight versus no weight in a strict equidistance calculation

Current Status

Since the Dominican Republic’s legislation and the United States’ and United Kingdom’s joint demarche in 2007, there has been little communication or clarification made public regarding the status of maritime space in the area.

Comments made in March 2018 by Chris Campbell, British ambassador to the Dominican Republic, implied the United Kingdom was awaiting clarification on the archipelagic status claimed by Dominican Republic, also acknowledging that these claims could lead to a territorial dispute.

So at this point the situation at Mouchoir Bank remains stagnant. The 1996 maritime boundary between Dominican Republic and United Kingdom (Turks and Caicos) continues to await (unlikely) ratification by either State, and at the time of this writing we have not heard of any clarifications or relevant communications between the parties involved regarding this maritime space.

Provisional Equidistance 101

November 14, 2018
Kevin Danaher

Maritime boundary claims are critically important for sovereign States, particularly when fossil fuel deposits, fishing grounds or other natural resources are involved. But what happens when two nearby States don’t have a defined maritime boundary? This is typically where the principle of provisional equidistance comes in.

When it comes to land boundaries, there are often natural borders – like mountains and rivers – that help delineate States. Countries can also physically mark the land to indicate a limit. In the maritime world, though, there’s not much to go off of. Thus, provisional equidistance is critical.

At a technical level, provisional equidistance is defined as a line that extends halfway between the coastlines of two countries. The goal is to equally divide the sea between the States, like so:

The provisional equidistance line between Yemen and Somalia divides the Gulf of Aden.

The grey line through the Gulf of Aden represents a provisional equidistance line between Yemen and Somalia.

Countries that are adjacent to each other, however, have a line that extends out from the coast at an angle determined by the details of the baseline (coast).

The provisional equidistance line between the U.S. and Canada.

The grey line is a provisional equidistance line between Canada and the United States.

It’s important to note that provisional equidistance lines are not official boundaries, as they lack a treaty or defining document behind them. Instead, they are drawn as a placeholder for a maritime boundary when one is not already agreed upon.

Looking at the literal definitions of each word of this term:

In other words, provisional equidistance as it relates to maritime boundary claims is the concept that countries should conform to the median line that is of equal distance between the opposing or adjacent country.

Origins of Provisional Equidistance

This idea of equally splitting up maritime space comes way before any legal document.

Imagine this scenario: Country A starts fishing too close to the coast of Country B. Country B asks Country A to stop, kicking off the dialogue of “who owns what” and prompting them to figure out a boundary.

Here lies the problem introduced before. There are no real markers on the surface of water to help delimit the boundary. Country B wants some sort of designation to avoid running into Country A during fishing ventures, but you can’t exactly build a fence in the ocean.

In the past, it was reasonable to just say “you stay on your half and I’ll stay on mine.”

That’s the line of provisional equidistance.

Today, it’s far more complicated because we have highly accurate GPS and navigational tools, and other pieces of advanced technology that paint a more detailed picture of maritime space and respective sovereignty. It’s much easier now to “see” the distinct line between countries, which means more potential for disputes to crop up.

But the concept of equidistance prevails. In fact, it’s rooted in the United Nations Convention on the Law of the Sea as a definitive concept to help guide countries in defining sovereignty where there are no agreements in place, and is therefore also a pillar in dispute resolution.

On page 30 of the document, Article 15 breaks down the “delimitation of the territorial sea between States with opposite or adjacent coasts,” describing provisional equidistance in a nutshell:

“Where the coasts of two States are opposite or adjacent to each other, neither of the two States is entitled, failing agreement between them to the contrary, to extend its territorial sea beyond the median line every point of which is equidistant from the nearest points on the baselines from which the breadth of the territorial seas of each of the two States is measured. The above provision does not apply, however, where it is necessary by reason of historic title or other special circumstances to delimit the territorial seas of the two States in a way which is at variance therewith.”

Examples of Provisional Equidistance in Practice

In many cases, this starting point eventually translates into a real, court-backed boundary, or one agreed to bilaterally between coutries. Let’s take Ghana versus Cote d’Ivoire, for example.

For over five decades, the neighboring countries respected an equidistance line between them in the Atlantic Ocean. Though this boundary was not recognized by a treaty, both countries accepted it, as demonstrated through oil agreements and other applications.

However, Cote d’Ivoire’s position of acceptance changed in 2009 – following Ghana’s discovery of significant quantities of oil on its side of the boundary.

Thus, five years of negotiations ensued as Cote d’Ivoire continued to propose different boundaries, all of which significantly cut into Ghana’s historically respected maritime space (based on equidistance) and threatened not only Ghana’s petroleum industry, but also the legal, political and economic stability of both countries.

The dispute also introduced uncertainty into the law of maritime delimitation. It threatened to establish a new precedent of countries abandoning historical boundaries in favor of more expansive claims, motivated by the discovery of oil on the other side.

In light of such implications, Ghana initiated proceedings with the International Tribunal for the Law of the Sea to set a real boundary that could be defined and enforced by the law – and in 2017, the two countries received a unanimous ruling that fixed the maritime boundary using a strict equidistance line … nearly identical to the one originally respected from 1960 to 2009.

Provisional Equidistance between Ghana and Cote d'Ivoire

The red line is the court-ruled maritime boundary (based on equidistance) between Cote d’Ivoire and Ghana.

Determining Baseline Points

In the Sovereign Limits database, we show “strict,” provisional equidistance in maritime spaces that lack an official boundary. No matter the coastline in question, the line is exactly in the middle without any alterations. This is to show the most neutral, wholistic visual of a country’s sovereign footprint.

Though maritime boundaries, like that ruled on between Ghana and Cote d’Ivoire in 2017, are often based off of the median line, things start to change once they begin to formally construct a boundary. Highly technical observations generate various lines depending on the size of a territory and details on the coast.

What happens to sovereignty if a country has a tiny rock island that disappears at high tide? What about when a flow of lava creates land right off the coast?

Many questions arise and several factors on the coast come into play when constructing a maritime boundary, and various scenarios of equidistance are often constructed to illustrate how they might impact a boundary..

Let’s look at an example of provisional equidistance between the islands of Vanuatu and the French territory New Caledonia:

Building equidistance between Vanuatu and New Caledonia.

Construction lines between the islands of New Caledonia and Vanuatu

Though there is no formal agreement in place, this detailed provisional equidistance line we generated for Sovereign Limits provides a nice snap shot of what could be.

As the image illustrates, provisional equidistance is much more than a line that cuts maritime space in half. It requires some research, accurate data and precise construction lines.

This line stretches equally between the two territories based off of many key contributing points on each coastline. We’ve derived these baselines in two key ways: using data from the National Geospatial-Intelligence Agency (NGA) and using coastlines digitized directly from satellite images.

The data is eventually processed in CARIS’s Limits and Boundaries module, to define the most accurate equidistance line possible based off of the baselines input.

Provisional Equidistance 101: Conclusion

Our goal for Sovereign Limits is to show a comprehensive picture of sovereignty for each and every country. So, whenever a land boundary meets the sea, we draw a line of provisional equidistance to indicate what adjacent countries might be entitled to should they reach a boundary agreement, as well as what boundaries, in theory, they should respect in lack of an agreed maritime boundary. For another exercise in equidistance, check out my recent post on the Spanish enclaves in Morocco.

What do countries respect in their daily operations? That’s a good question. Provisional equidistance is a great place to start.

Interested in looking at other examples of provisional equidistance? Explore our international boundary database today.

The Spanish Enclaves in Morocco: An Assessment of Potential Maritime Space

October 29, 2018
Kevin Danaher

The Plazas de Soberanía

Along Morocco’s Mediterranean coast, Spain has long maintained sovereignty over several small territories, described herein as “the enclaves”. These are Perejil Island, Ceuta, Peñón de Velez de la Gomera, Islas Alhucaimas, Melilla, and Islas Chafarinas: collectively known as the Plazas de Soberanía. Three of these share land boundaries with Morocco, while the others are islands just off the coast. Despite their recognition of Morocco as an independent state in 1956 and the dissolving of the Spanish protectorate there, the enclaves have been sustained as territories of Spain and are administered as if part of it. Even so, Morocco has openly disputed Spanish ownership of the enclaves, and a 1975 straight baseline claim published by Morocco encompasses all of them. The western-most disputed feature, Perejil Island, is located just off of the Moroccan coast and is of note because it was the site of an armed incident between Spain and Morocco in 2002.

An overview of the Plazas de Soberanía

Since 1977, Spain has claimed a twelve nautical mile territorial sea from the shores of its mainland and territories, however the state has made no explicit maritime claims relating to the enclaves on the African continent. Given Morocco’s negative view on the Spanish possession and occupation of the enclaves, it is extremely unlikely that the two states would pursue any bilateral discussions on maritime space surrounding them. There is also little precedent for establishing maritime boundaries surrounding enclaved territories or possessions, especially the size of these. In the Mediterranean we could look to the island of Cyprus, where the United Kingdom claims a three nautical mile territorial sea from their sovereign base areas Akrotiri and Dhekelia, and a 1960 bilateral agreement established maritime boundaries with Cyprus following a path of simplified equidistance (of course, a key difference is that there is no dispute over the UK’s possession of these bases). We could also look to Monaco, which, from a 1984 agreement with France, gets a several-kilometer wide corridor out into the Mediterranean almost 50 nautical miles. However, Monaco is an independent, self-governing state and not a territory, so despite its size this example isn’t truly comparable either.

Drawing comparison within the Mediterranean. left) The United Kingdom’s established maritime boundaries with Cyprus for Akrotiri and Dhekelia. right) Monaco’s maritime boundary with France.

But, in the off chance that bilateral talks took place, what might maritime space around the Spanish enclaves look like? To begin to explore this question, I’ve plotted strict equidistance between the enclaves and Morocco, as well as potential territorial sea limits from each. These are explored in map form below, moving from West to East along the Moroccan mainland.

An Assessment of Potential Maritime Space

Perejil Island

Equidistance between Perejil Island and Morocco closes in on itself fairly rapidly. This island was the site of an armed incident between Morocco and Spain in 2002.


Due to its location at the mouth of the Mediterranean and proximity to Spain, equidistance between Ceuta and mainland Morocco would converge with equidistance between Morocco and the Spanish mainland, expanding Spain’s potential maritime Space near the Strait of Gibraltar.

Peñón de Velez de la Gomera

Equidistance lines quickly converge to cut off Peñón de Velez de la Gomera just over 4 nautical miles from the fort.

Islas Alhucemas

Made up of islands Peñón de Alhucaimas. Isla de Tierra, and Isla del Mar, equidistance between Las Islas Alhucaimas and mainland Morocco also quickly closes in on itself.


Melilla, similar to Ceuta in size and length of land boundary with Morocco, is cut off by equidistance with the Moroccan mainland just over 9 nautical miles from its coast.

Islas Chafarinas

Las Islas Chafarinas (made up of Isla del Congreso, Isla Isabel II, and Isla del Rey) is the only other territory aside from Ceuta in which an equidistance line with mainland Morocco does not quickly close in on itself. In this scenario, the course of equidistance continues on in the direction indicated by the arrows to 1) intersect a provisional equidistance line between mainland Morocco and Algeria and 2) converge with an equidistance line between Morocco and the Spanish mainland to the North. Given the proximity of Islas Chafarinas to the Moroccan mainland, it is highly unlikely they would be allowed a connection to the maritime space of mainland Spain, or to influence an Algeria-Morocco maritime boundary. So, above we see three and twelve nautical mile limits from the islands, which might cap off the islands’ potential maritime space (the Sovereign Limits database draws an implied maritime limit for Islas Chafarinas at the 12M limit, enclaving it).

Final Thoughts

For the purposes of the Sovereign Limits database, we show disputes as they exist, acknowledging their presence but staying neutral to show a situation without taking one side or the other. We draw equidistance in maritime space using the principle that the land dominates the sea. This means equidistance lines are steered entirely by the configuration of the coast, and they begin from the point where a land boundary meets the shoreline. The Spanish enclaves are in one of the more unique categories of potential maritime disputes because they are enclaves. Morocco surrounds these areas entirely, which means if at some point Morocco gained possession of them, these invisible lines delineating borders and maritime space would disappear entirely.

The history of some of the Plazas de Soberanía goes way back, and is quite interesting to read up on.

Sentinel Imagery @ ESA

How Newly Formed Land Might Affect the Territorial Sea

August 12, 2018
Kevin Danaher

Many are aware of the recent eruption of the Kilauea Volcano on the island of Hawai’i. The lava flows this eruption has produced have entered the ocean at several locations, expanding the island’s shoreline and even creating a small new island offshore. As an individual who has spent many a working hour assessing how shorelines (or normal baselines, as they are referred to under the Law of the Sea) will impact territorial sovereignty and boundaries with neighboring countries, I thought it would be an interesting exercise to assess how this latest eruption could affect the sovereign limits of Hawaii and the United States.

The island of Hawaii, showing locations of the volcano summit and Active Fissure 8, the origin of recent lava flows.

To begin this exercise, I pulled an island polygon for Hawai’i from an early June edition of OpenStreetMap — prior to the eruption. I then pulled the same feature from the latest OpenStreetMap. It speaks volumes to the power of OpenStreetMap and dedication of its contributors that the lava flow areas and expanded shoreline have been added and updated since the eruption in early July.

Active lava flows and ocean entry, showing area of expanded shoreline since the eruption.

An area measurement of the land added since the eruption yields about three sq. km. (shown in dark red on the map above). To assess the impact of the expanded shoreline on the 12 nautical mile territorial sea, I ran two simple “envelope of arcs” calculations in CARIS software (their Limits and Boundaries module). For one calculation I used a pre-eruption normal baseline, and for the other a post-eruption normal baseline. With each calculation, I was able to identify the contributing base points along the normal baseline as well as construction lines emanating from each to create the 12 nautical mile territorial sea limit.

Calculation of 12 nautical mile territorial seas showing contributing base points along the new and older shoreline, construction lines, and the territorial sea limit.

In this real-world example, the expanded shoreline of the island adds about nine square kilometers to the territorial sea area of the island of Hawai’i.

So does this mean there is a direct correlation between newly formed land and area added to a country’s sovereign space? Not really. In the case illustrated above, the expanded shoreline has been built out seaward enough on a slightly convex coast that it adds new contributing base points to the 12 nautical mile territorial sea. However, if the lava were entering the ocean in an area of coastal concavity, bay, or inlet, we might see several square kilometers of new land that does nothing to change the outer limit of the territorial sea.

Diagram illustrating lava filling in a coastal concavity, versus lava expanding on an area of coastal convexity. The latter might contribute to an expanded territorial sea.

Of course, this new “land” created by the eruption is quite fragile and susceptible to collapse and rapid breakdown, so just as quickly as we’ve added 9 square kilometers to the United States’ sovereignty, it could get washed away.

The island formed by lava flow in last month’s eruption. Photo @ USGS

Map data @ OpenStreetMap

Newly Signed Maritime Boundary Closes “Gap” in the Timor Sea

March 14, 2018
Kevin Danaher

On March 6, 2018, Australia and Timor-Leste signed a treaty establishing a maritime boundary in the Timor Sea. The oil-rich maritime area in question had been a source of conflict leading up to Timor-Leste’s independence in 2002, with tensions between this tiny country and its larger neighbor to the south only growing worse since. In negotiations, Australia sought a boundary along its continental shelf, while Timor-Leste aimed for a median line dividing the maritime space between the two. In 2016, Timor-Leste filed a “notice instituting conciliation” with the Permanent Court of Arbitration (PCA), which has since facilitated negotiations between the two nations to resolve the dispute. It is of note that this was the first ever PCA conciliation to be initiated under the UN Convention on the Law of the Sea, and it has successfully led to a bilateral maritime agreement.

The new continental shelf boundary is made up of 13 points (TA-1 through TA-13), all of which are connected by geodesic lines, and the exclusive economic zone boundary is defined by five of these (TA-5 through TA-10), with the eastern half of the EEZ boundary following the principle of equidistance. On both sides, the continental shelf boundary abuts existing “zones of shared sovereignty” in place between Australia and Indonesia. Within these areas, Australia maintains rights to the seabed and Indonesia to the EEZ/water column. This arrangement between Australia and Indonesia stems from 1972 and 1997 agreements, from which the newly established Australia-Timor-Leste boundary has gleaned several of its turning points.

Map depicting the new Australia-Timor-Leste boundary, as well as zones of shared sovereignty between Australia and Indonesia. Dashed blue lines are strict equidistance lines.

Due to the existence of shared sovereignty zones and the history of delimitations between Australia and Indonesia in the Timor Sea, an interesting term is found in Article 2 of the treaty: It defines several of the continental shelf boundary segments as “Provisional.” The treaty elaborates on this in Article 3, essentially making accommodations for a future delimitation between Timor-Leste and Indonesia by allowing the “Provisional” segments defined in Article 2 to be adjusted under certain conditions.

A major aspect of the treaty involves existing oil fields and the dividing of oil revenue. The path of the maritime boundary leaves Timor-Leste with sovereignty over several oil fields previously shared with Australia in the now-defunct Joint Petroleum Development Area (defined in 2002 by the Timor Sea Treaty). A “Special Regime Area” is now defined surrounding the Greater Sunrise Fields, and the treaty includes language to split revenue from these fields depending on where oil is piped and processed, however always in favor of Timor-Leste.

Map depicting the Greater Sunrise Fields and the delimited Special Regime Area. Source: Annex C, Treaty between Australia and the Democratic Republic of Timor-Leste Establishing their Maritime Boundaries in the Timor Sea.

The establishment of a maritime border and signing of a treaty is seen as a great win for stability in this region, and especially for the country of Timor-Leste, which has come away with solidified sovereignty over known oil reserves — a potentially major stimulus to a long-struggling economy. However, the treaty also raises some questions; How will boundary negotiations go between Indonesia and Timor-Leste? And, based on the outcome of the Australia – Timor-Leste treaty, will Indonesia attempt to renegotiate its maritime boundaries with Australia?

A full version of the treaty can be accessed here.

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