Publication Date: 2020-07-29

Approval Date: 2020-06-23

Submission Date: 2020-05-27

Reference number of this document: OGC 20-013r4

Reference URL for this document:

Category: OGC Public Engineering Report

Editor: Jonathan Pritchard

Title: OGC Maritime Limits and Boundaries Pilot: Engineering Report

OGC Public Engineering Report


Copyright © 2020 Open Geospatial Consortium. To obtain additional rights of use, visit


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Table of Contents

1. Introduction

The Open Geospatial Consortium (OGC) Maritime Limits and Boundaries (MLB) Pilot is a project designed to advance the implementation of a data model, architecture, and prototypes for use with the creation, management, integration, dissemination, and onward use of official data for maritime baselines, limits, zones, and boundaries. It also aims to enable, by extension, the "reuse" of such data within far broader geo-regulation contexts.

The Pilot has emerged from activities of the sponsoring organizations; namely the Canadian Hydrographic Service, Natural Resources Canada, Geoscience Australia, and the United Kingdom Hydrographic Office, who have participated in the development of the International Hydrographic Organization (IHO) standard IHO S-121. The OGC has a general Memorandum of Understanding with the IHO covering collaboration on development of standards and matters of common interest. Under the MOU the OGC seeks to bridge gaps relating to marine standards with other groups and domains.

The original reasons why the Pilot came into being were to build a detailed implementation of the S-121 standard, to test productionization of its many different facets, and to demonstrate its potential in a broader context. The Pilot was designed to build on the progress made in baselining the S-121 standard and to test the practicality and potential of its features. The Pilot has been driven by its sponsoring organizations and built advanced implementations alongside participating industry representatives using OGC standards, architecture and best practices.

These activities use the scope of S-121 as a foundation but seek to engage the broader georegulation community and contribute to the evolving standardization efforts in these broader domains. The tangible advantages of taking a lead in this evolution is the prevention of rework and the harmonization of features between S-121 (as defined in the IHO Geospatial registry) with those from other domains which may be similar in nature but not specifically marine in nature.

The Pilot is being carried out by the OGC employing its own internal defined approval process for deliverables including a review and approval cycle with interested Domain Working Groups within the OGC Technical Committee. Delivery to sponsors, by the OGC, will then take place to the sponsoring organizations to meet their stated requirements as defined in the Call For Participation. The IHO S-121 Project Team, a subgroup of the IHOs S-100 working group, have been involved through the reciprocal participation of multiple project members and sponsors and their respective organizations and have all contributed to the defined Pilot goals. The sponsoring organizations have been responsible for defining the requirements and deliverables and are the prime customers of the Pilot.

This is the first Pilot to have been run in this way within the OGC and is unique in many ways. It has taken a standard defined by another global standards development organization (SDO), and integrated it with an OGC baseline, opening up its modeled content to the full range of OGC web services and architectures.

There are two goals of the S-121 standard, first: to have an open, international, coordinate-based, representation of maritime boundaries and their associated rights, restrictions, and responsibilities (RRRs) that are authoritative and easy to interpret. The second goal is to facilitate the deposit of maritime boundary claims with the Division for Ocean Affairs and the Law of the Sea (DOALOS) in a spatial coordinate-based format that fulfills legal requirements under UNCLOS. The Division for Ocean Affairs and the Law of the Sea (DOALOS), of the Office of Legal Affairs of the United Nations, approached the International Hydrographic Organization with a request to identify appropriate technical standards. After consultations, the S-121 project team was formed by Member States of the International Hydrographic Organization and, accordingly, S-121 was created.

As an IHO Standard within the S-100 framework, and by sharing ISO19152 components, the standard contributes to both the goals of open standards and facilitating depository obligations as well as contributing to broader goals in the Marine Spatial Data Infrastructure (MSDI) community and the IHOs allied organizations including the evolving field of marine georegulation.

The MLB Pilot initiative thus begins with an implementation model, encoding, architecture, and prototypes for sharing Maritime Limits and Boundaries (MLBs) between digital systems compatible with the structures of S-121. Techniques and samples of natural extensions to the encoded data are also proposed to contribute to the longer-term roadmap. This was accomplished by enabling reuse of data through OGC standard web services and enabling use of ISO19152 conceptual model and structures in the related domains.

2. Executive Summary

This document comprises the Engineering Report (ER) and documents the activities under Phase 1 and Phase 2 of the OGC Maritime Limits and Boundaries (MLB) Pilot.

This Engineering Report details the activities undertaken by participants in the pilot, the data supplied, transformed, and used to demonstrate the pilot’s objectives, and the results of the various interoperability tests performed within the pilot. Also documented here are the various outputs from the pilot activities, where they are directed, and where updates or clarifications are recommended to external standards or other elements of the broader ecosystem.

The ER documents the journey taken within the project, from its origins as an architectural statement of intent, through to the definition of its core elements (the GML application schema which lends a common language to the data) and the implementation of that schema within COTS, open source and bespoke software elements. The engineering report also summarizes the outputs from the process, any unresolved issues, and potential enhancements for the future.

2.1. Overview of Pilot Activities

The MLB Pilot is about data, the standards used to define it, its content definition, and its path from originating producers to a variety of end users.

The main activities of the Pilot were the following.

  • Productionizing S-121 data production by creating an initial Application Schema which enables the encoding of S-121 data in Geographic Markup Language (GML), a dialect of XML specifically designed for encoding geospatial data. The existing S-121 standard does not contain an encoding of this nature, only a text encoding designed for its core use case.

  • Transformation of representative datasets into the GML encoding defined.

  • Onward use of the GML data within several OGC Standard web services and its transformation to a text form specific to S-121 use cases.

  • Extension and incorporation of S-121 data alongside data from other domains.

The flow of this engineering report reflects the flow of data through the various artefacts, tools, and systems defined above and used in the Pilot. The idea is to illustrate each of the components in detail as major sections within the ER. The diagram below thus shows the data flow through the Pilot as defined in detail by the architectural model in the call for participation.

The pilot’s activities are a significant achievement in several ways:

  • It is the first systematic implementation of S-121 (and extensions to it) using a variety of different organizations' data in different forms;

  • It exercises all the different facets of the S-121 standards including geospatial feature realization and defining LADM structures in conformance with S-121’s implementation of ISO19152;

  • It successfully blends IHO feature content and encoding with OGC standards and web services broadening dramatically the number of onward uses and participants for the data content; and

  • It shows how multiple domains can be combined in GML encoded content.

Figure 1. Data flow through the various components of the Pilot

Reading out the data flow from left to right, the diagram shows the following.

  • Data, within the pilot this is MLB data in various "database" forms, conforming to internally adopted standards, models, and potentially expressing different aspects of definitions contained in the S-121 standard.

  • Transformation (the "T" boxes) into GML conformant with the Pilot GML Application Schema via either COTS tools (from both the hydrographic domain and mainstream GIS) and bespoke software created during the Pilot. GML is validated, again using either bespoke or COTS packages against the schema and open standards.

  • Onward use for:

    • Direct use of GML via COTS and open source GIS packages;

    • Population of CSW services from metadata built specifically for the certain datasets; and

    • Promulgation via core OGC Web services, WFS and WMS.

  • Production of Human Readable Text (including validation against source GML data) from the transformed GML.

  • Validation of the HR Text against the original GML.

2.2. Selection of Key Findings.

The Pilot produced a number of outputs, a summary of which are presented here. The key deliverables were schemas which allow the S-121 model contained in the IHO standard to be expressed and validated in a precise, technical format. Mechanisms for extending the domain of the core schema were developed, tested, and demonstrated and data supplied by sponsor organizations was transformed into conformant GML to test a range of onward uses.

2.2.1. GML Application Schema

  • The IHO S-121 product specification has been published at version 1.0.0. This represents a significant step forward for its development and for the community driving it. The product specification included a draft S-100 feature catalogue which expresses the core features, attributes, relationships, and metadata in precise IHO terms. This feature catalogue was baselined at the same time as the product specification and forms the basis of the creation of the S-121 GML Application Schema within the Pilot.

  • The construction of a GML Application Schema has been successful.

    • The GML Application Schema has produced a viable encoding for data conforming to the S-121 model, and for related data by extension. The Schema has been baselined for both IHO S-121 content and for an initial extended vocabulary.

    • The schema has used the IHO S-100 GML Profile, is conformant with that profile, and interoperable with the software tools and systems used by the participants within the project from both IHO specific applications and broader GIS tools, both proprietary/COTS and Open Source.

  • The Application Schema developed required several design decisions to be made which could arguably have been more tightly specified within the S-100 GML Profile. Since S-100 defines a comprehensive XML feature catalogue structure it would be feasible to map that to a GML Application Schema in a much more specific way in order to take out the ambiguity of the schema development. Particular areas where the profile could benefit from this extra specificity have been noted in the report, particularly:

    • Dataset aggregation and definition;

    • Names of complex types;

    • Dataset layout e.g., the order of geometry, information types, feature types;

    • Conventions for enumeration value inclusion;

    • Conventions for relationship definition; and

    • Guidance on norms for multi-lingual support within the application schemas.

  • Additionally, the GML Profile contained in Part 10b of S-100 may benefit from some modernization/update, particularly the definitions of DSID/DSSI content and identifiers. These, and other items, will be discussed with the S-100WG at a suitable upcoming meeting.

  • The Schema has been thoroughly tested with sponsor data including complex examples such as the LADM structures, dual positional representation, and extensions into other domains. The data transformation technologies and their subsequent onward usage of data within OGC services demonstrate practically the utility of an "implementation first" approach. This approach focused on practical, rather than theoretical initiatives and working practices and concentrated on producing working prototypes rather than theoretical models and documents.

  • S-121 is a complex standard which implements both S-100 and ISO 19152 structures and norms. The Pilot demonstrated the various features of the S-121 model contained in the product specification as far as resources allowed and the GML Schema constructed represents the extents of that testing process. As S-121’s implementations grow, the Pilot activities will form a valuable source of guidance and knowledge for those wishing to express and use MLB data for a variety of purposes.

2.2.2. ISO 19152 and LADM Implementation

  • The S-121 standard includes discrete packages representing geospatial features, ISO 19115 metadata for their sources, and ISO 19152 structures for representing LADM structures attached to them. Participant data expressing combinations of all of these were constructed in the project and this provides an overview of the challenges and complexities with S-121. As a GML encoding of the data, the project has encapsulated the data supplied and shown example implementations, but these are just a start. The ability to encode these structures in a representative way requires encoding guidance. The IHO Data Classification and Encoding Guide for S-121 is currently at version 1.0.0 and as it matures it will be a valuable manual for populating S-121 data. The project has shown that sponsors have a great disparity in how their own data structure aligns with the definitions within the standard and the amount of transformation necessary to achieve truly conformant S-121 GML.

  • Project activities focused within Phase 2 centered around exercising all the features of the GML Application Schema. In particular, the implementation of the LADM package entails a complex series of information types and relationships with them implementing the relevant ISO 19152 provisions. This complexity led to a thorough investigation of all aspects of implementation which can feed into recommended guidance for future implementers of IHO S-121.

  • The ISO 19152 package within the S-121 product specification provides a broad conceptual framework for Rights, Responsibilities, and Restrictions which is, in the S-121 context, restricted to the domain of UNCLOS features. The project has developed a generic extension mechanism for the GML Schema which allows co-existence of features and relationships between them which will enable the LADM aspects to be extended to arbitrary domains such as Hydrocarbons and Fishing Limits. This mechanism will be promoted further post-project closure and the modular structure arrived at should be used as an input both to IHO and the developing ISO community.

2.2.3. Web Services

  • Data transformation into GML enables its use within web services such as WFS, WMS, and for search and retrieval, via CSW along with structured metadata population and processing. These have all been demonstrated by project activities and, where possible, included in detail within this ER.

  • These web services are able to process the complex GML produced and also deal with the S-121 specific elements, such as complex multi-lingual naming and textual position encoding.

  • This process of opening data via OGC web services is the foundation for MLB data to sit alongside other geo-regulation datasets within current and future web services. OGC’s evolution of web services into API based interfaces would be consistent with the approach taken by the Pilot.

2.2.4. Human Readable Text

  • Production of a multi-lingual Human Readable Text rendering of GML Data has been achieved to a high level of detail. This development process has shown the viability of transformation from a sponsor-specific database into textual form which meets requirements from stakeholders and is a basis for taking forward with the S-121 community.

  • Validation of the HR Text outputs against source data has been achieved to a high degree of detail as well. This contributes to the general area of validation alongside standard XML/GML validation by providing a reconciliation of produced HR text features with their original source.

  • The HR text outputs can be easily manipulated into multiple other forms such as pdf and HTML as required.

2.3. Background

2.3.1. UNCLOS

The United Nations Convention on the Law of the Sea (UNCLOS), also called the Law of the Sea Convention or the Law of the Sea treaty, is the international agreement that resulted from the third United Nations Conference on the Law of the Sea (UNCLOS III), which took place between 1973 and 1982.

The Law of the Sea Convention defines the rights and responsibilities of nations with respect to their use of the world’s oceans, establishing guidelines for businesses, the environment, and the management of marine natural resources. The Convention, concluded in 1982, replaced the quad-treaty 1958 Convention on the High Seas. UNCLOS came into force in 1994, a year after Guyana became the 60th nation to ratify the treaty. As of June 2016, 167 countries and the European Union are parties to the convention.

2.3.2. IHO and S-121 Background

Coastal States, under articles 16, 47, 75, 76, and 84 Convention, are required to deposit with the Secretary-General of the United Nations charts showing: straight baselines, including closing lines of mouths of rivers and bays, and archipelagic baselines; the outer limits, as well as lines of delimitation between States with adjacent or opposite coasts, of the territorial sea (including roadsteads, article 12); the contiguous zone; and the exclusive economic zone and the continental shelf. Alternatively, the lists of geographical coordinates of points, specifying the geodetic datum, may be substituted.

In its resolutions 49/28 of 6 December 1994 and 52/26 of 26 November 1997, the General Assembly requested the Secretary-General to establish appropriate facilities, as required by the Convention, for the deposit by States of maps, charts, and geographic coordinates concerning national maritime zones and establish a system for their recording and publicity and to develop and maintain [such] facilities for the deposit by States of charts and geographical coordinates concerning maritime zones, including lines of delimitation, and to give due publicity thereto, as required by article 16, paragraph 2, article 47, paragraph 9, article 75, paragraph 2, article 76, paragraph 9 and article 84, paragraph 2, of the Convention. The Division for Ocean Affairs and the Law of the Sea, Office of Legal Affairs of the United Nations is the unit of the Secretariat which performs these depositary functions on behalf of the Secretary-General, as part of an integrated program on the law of the sea and ocean affairs, distinct from the usual depositary functions of the Secretary-General in respect to multilateral treaties.

Subsequently, in its resolution 59/24 of 17 November 2004, the General Assembly requested the Secretary-General to improve the existing geographic information system for the deposit by States of charts and geographical coordinates concerning maritime zones, including lines of delimitation in particular by implementing, in cooperation with relevant international organizations technical standards for the collection, storage and dissemination of the information deposited, in order to ensure compatibility among the Geographic Information System, electronic nautical charts, and other systems developed by these organizations. Recent General Assembly resolutions have noted ongoing efforts in this regard.

In 2015 the UN passed resolution A/RES/70 nominating a set of 17 Sustainable Development Goals (SDGs). Target C of SDG 14 encourages states to "Enhance the conservation and sustainable use of oceans and their resources by implementing international law as reflected in UNCLOS." The indicator 14.C.1 is "the number of countries making progress in ratifying, accepting and implementing through legal, policy and institutional frameworks, ocean-related instruments that implement international law, as reflected in the United Nation Convention on the Law of the Sea, for the conservation and sustainable use of the oceans and their resources." This work is required in order to assess indicator 14.2.1: "Proportion of national exclusive economic zones managed using ecosystem-based approaches."

In addition, the General Assembly, in its annual resolutions on Oceans and the law of the sea, calls upon States Parties to the Convention to fulfill their deposit obligations. Most recently, General Assembly resolution 71/257 of 23 December 2016 calls upon States Parties to the Convention that have not yet done so to deposit with the Secretary-General charts or lists of geographical coordinates, as provided for in the Convention, preferably using the generally accepted and most recent geodetic datums (para. 6).

To facilitate the implementation of the Secretary-General’s depositary functions, coastal States are encouraged to deposit the following information, as a minimum.

  • Geographic coordinates of points in decimal degrees on the straight baselines and archipelagic baselines in common global geodetic datum such as WGS 84, accompanied, as appropriate, by the relevant national legislation.

  • Geographic coordinates of points in decimal degrees on the outer limits as well as lines of delimitation between States with adjacent or opposite coasts for the following maritime zones: territorial sea (including roadsteads); contiguous zone; exclusive economic zone and continental shelf, in common global geodetic datum such as WGS 84, accompanied, as appropriate, by the relevant national legislation. Ideally the points defining the outer limits should be close enough to each other to ensure that the line formed by connecting the points with geodesic lines accurately reflects the outer limit of the maritime zone(s). States Parties are also encouraged to identify in the deposit the points that are part of an international boundary. States Parties are further encouraged to accompany such deposits with the relevant national legislation and/or with references to relevant international treaties.

Accordingly, the Division for Ocean Affairs and the Law of the Sea, of the Office of Legal Affairs of the United Nations, the unit entrusted with carrying out these responsibilities on behalf of the Secretary-General, approached the International Hydrographic Organization with a request to identifying appropriate technical standards. After consultations, the S-121 project team was formed by Member States of the International Hydrographic Organization.

S-121 is an open access method of providing digital representation of Maritime Limits and Boundaries (MLBs). Maritime limits and boundaries are constructs used to define maritime zones for nations around the world. With the United Nations Convention of the Law of the Sea (UNCLOS), they can form an international legal foundation of the marine domain. S-121 represents an essential extension of the International Hydrographic organization S-100 for the administration of the marine domain.

In December 2016, the International Hydrographic organization (IHO) distributed the initial document describing the standard at the United Nations headquarters in New York. This meeting began the international effort to define the core features of the S-121 standard.

There are two goals of the S-121 standard, first: to have an open, international, coordinate-based, representation of maritime boundaries. The second goal is to facilitate the deposit of maritime boundary claims with the Division for Ocean Affairs and the Law of the Sea (DOALOS) in a spatial coordinate-based format that fulfills legal requirements under UNCLOS.

2.3.3. Broader Uses of the S-121 Standard

Although S-121 is defined primarily within the narrow constraints of a subset of the UNCLOS Convention, the broader conceptual area of marine georegulation and marine spatial planning is an emerging area important to the marine geospatial community. Wikipedia defines Marine Spatial Planning (MSP) as "a process that brings together multiple users of the ocean – including energy, industry, government, conservation and recreation – to make informed and coordinated decisions about how to use marine resources sustainably. MSP generally uses maps to create a more comprehensive picture of a marine area – identifying where and how an ocean area is being used and what natural resources and habitat exist," although the definition of exactly what these uses are vary from region to region.

The areas of jurisdiction defined under UNCLOS, particularly the Territorial Sea Area, Contiguous Zone, and Exclusive Economic Zone, together with associated limits and baselines play an important role in marine georegulation and marine spatial planning as they define the geographic areas on which any legal regime is predicated. In contrast to UNCLOS, Marine Spatial Planning is a term which has many interpretations and definitions but its link with the UNCLOS-defined elements is present in all of them. The S-121 model, therefore, has a central part in these activities and the data used to express these concepts. The S-121 model also contains important interfaces to compatible structures which model ISO19152, the Land Administration Domain Model and a comprehensive source information repository on a per-feature basis which can enable the use of S-121 data in integrated marine cadastral applications conformant with international standards.

In order to increase interoperability with other domains of expertise, both in the georegulation field and marine spatial planning, phase 2 of the Pilot has considered the concept of "extending" the framework on which the S-121 model is realized in the GML Application Schema. This extension does not seek to modify or change the essential S-121 data but instead allow other domains to be co-located with its data in a single dataset. The mechanism for doing this has been evolved during Phase 2 of the project and is presented along with the other project outputs and using sponsor data to illustrate the potential. The potential here is not limited purely to the marine domain.

The implementation of ISO19152 within S-121 and the extension mechanism formulated within the Phase 2 of the project does not require co-existence with marine domain data. Thus, terrestrial and land cadastral data can equally be represented alongside marine domain data in combined datasets.

2.3.4. ISO 19152

The ISO 19152 standard is a conceptual model which represents the domain of land administration, specifically rights, responsibilities and restrictions (RRR) affecting land and water. It has two overall goals:

  • An extensible basis for the development of land (and, by implication, water) administration systems; and

  • The enablement of communication between interested parties those structures contained within the model based on a shared vocabulary.

2.3.5. IHO, S-100 and S-121

The S-121 standard has been under development for some time and this section of the ER contains a broad overview of its origin, aims, and features relevant to the project. As documented in the previous section of this ER, the development of S-121 has been coordinated by an IHO project team under the S-100 working group (S-100 WG). IHO S-100, the framework standard used to define S-121 has been under development since the publication of its predecessor, IHO S-57 in 2001. IHO S-57, the current standard for the encoding of Electronic Navigational Charts under the SOLAS convention is a vector based standard developed specifically for the purpose of encoding charts for the purpose of safe navigation but S-100, conceived shortly afterwards represented a much bigger step forward.

S-100 aimed to overcome many of the perceived shortcomings of the newly released S-57 standard and was defined as a much broader standard where a framework of ISO-like structures was defined leaving the details of content and encoding to the authors of specific product specifications which would then sit alongside the main framework. S-100 therefore had the following goals:

  • Production of a standard in close alignment with the ISO19100 framework;

  • A framework standard which defines content through individual product specifications;

  • A separation of data content from its representation in encodings;

  • Fully machine-readable standards for both feature content and portrayal;

  • The location within a registry located at the IHO, of features, their attributes and metadata; and

  • The facility to update feature content and portrayal by end user systems.