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Main Page Project Team Standard Implementation Exchange Formats Documents UNCLOS S-100


The documents you find on this wiki site are "works in progress", they are in the process of being drafted and do not represent official statements either of the IHO or of the member states represented by the participants in this group.

The official IHO Downloads page is the repository for completed standards which are approved by member states.


The primary purpose of S-121 is to allow States to communicate official digital representations of their maritime limits and boundaries to the public and international community. The standard is designed to be acceptable as a method for States to fulfill their deposit obligations under the Convention. S-121 is established to depict, describe and communicate national maritime limit or boundary positions without prejudice to maritime boundary disputes. S-121 does not seek to resolve disputes between States: Where disputes exist, the standard will facilitate visibility of those disputes by allowing each party to publish its own position. The S-121 secondary purpose is to provide a flexible and expandable framework able to support other maritime delimitation requirements such as defining areas of overlapping jurisdiction and Joint Development Areas, or any other management areas.

The current vision for this standard is to leverage the capabilities of the ISO-19152 Land Administration Domain Model. ISO-19152 supports the legal description of associated rights, restriction and responsibilities along with providing proper referencing through sourcing and versioning. This additional capability aligns the standard with legal practices of trace-ability. The use of the ISO-19152 standard leverages the significant community investment made in land administration, with which the management of maritime boundaries and limits has much in common. The use of ISO-19152 provides a foundation to extend S-121 into the management of other regulated boundaries, such as marine reserves and fisheries. Alignment with the land domain model will facilitate consistent administration of the littoral zone for those states that adopt S-121 for their marine spaces and ISO-19152 for their land jurisdiction.

The S-121 standard is designed to provide a flexible management and communication solution that can support any type of MLBs for the broadest range of users including the Owner State, other States, the international community, government organizations, courts of law, private industry, academic institutions, and the general public. By construction, the standard also remains compatible with S-101 (Electronic Nautical Chart Product Specification) to allow for the depiction of the MLBs information encoded by the standard to be displayed in electronic navigation charts.

The S-121 takes a practical step toward achieving the vision of S-100 as it was established: to expend the user base and better accommodate the requirements of our digital world. By building on ISO-19152, the S-121 framework provides the capacity to more efficiently and consistently administer across the land and maritime domains. It is essential that we evolve current practices to provide a foundation for sustainable administration of the world’s blue economy. Use of the S-121 standard will reduce costs of enforcement and compliance, and will support the extension of the digital economy into the offshore.

Product Specifications

The key output from the S-121 project team is the S-121 standard itself. This is a product specification meeting the requirements set out in IHO S-100. The current editor's draft version of the standard together with supporting documents are held below.

S-121 Standard Components
Name Link Version Date
S-121 Cover Page Cover Page 3.0 12th June 2017
S-121 Draft Overview Draft Overview 3.0 17th April 2017
S-121 Draft Product Specification Draft Product Specification 3.0 17th April 2017
S-121 Draft S-121 Encoding Encoding - -
S-121 Feature Model Feature Model - 10th May 2017
MLB Features Features - Diagram - -

Schema in Enterprise Architect format

An HTML version of the S-121 / MLB feature model is now available from the following link.

HTML Interactive Model

The Enterprise Architect model will be available soon.

Standard Overview

Our planet’s oceans are subdivided by international and national laws into many zones. At the highest level, these zones define where States exercise sovereignty and sovereign rights, and identify areas beyond national jurisdictions that fall under international jurisdiction.

Maritime Limits and Boundaries (MLBs) are the constructs used to delineate maritime zones and forms the legal foundation of the marine domain. These maritime zones are established in law by their geographic limits .

To effectively distribute MLBs for the due publicity obligations under the Law of the Sea Convention and operational purposes, there needs to be a standard framework which ensures compatibility between users and encodes the legal character of the MLBs.

The Law of the Sea Convention says that:

  “Coastal States, … are required to deposit with the Secretary-General of the United Nations charts showing straight baselines and archipelagic 
   baselines as well as the outer limits of the territorial sea, the exclusive economic zone and the continental shelf; alternatively, the lists of 
   geographical coordinates of points, specifying the geodetic datum, may be substituted. Coastal States are also required to give due publicity to 
   all these charts and lists of geographical coordinates.” 

The S-121 standard needs to provide a set of feature types and an attribute structure that allows for the representation of the legal aspects of MLBs. These features can be included within “charts” or can be represented separately for deposition as “lists of geographical coordinates of points”.

The deposition of “charts” may be printed paper charts or images of charts. Specialized certified equipment is required for reading IHO S-57 or S-101 Electronic Nautical Charts (ENCs) and these charts are not directly readable without this specialized equipment. However, ENCs are read by mariners in a navigational context and when Maritime Limits or Boundaries are shown on ENCs they need to be derived directly from the features and attributes that are included in a deposit to the UN.

Class Derivation

Derivation from ISO 19152

Derivation from S-100 to S-121

Core Feature Objects and Code Lists

Files held in this wiki

  • Filelist - List of all files held within this wiki. In general files should be included as links in the appropriate wiki page.