Specialised Chart

Introduction

Specialised charts are maritime cartographic documents designed to meet a specific requirement that goes beyond the conventional use of a nautical chart. They are used to represent particular information, a specialised geographical area, a maritime phenomenon or a technical issue requiring dedicated cartographic treatment.

The “Specialised Charts” category at Nautic Way Maritime Bookshop therefore brings together documents designed to complement conventional nautical charts. Their purpose may be the preparation of an ocean passage, the study of a maritime area, the analysis of waters under national jurisdiction, the understanding of a geographical or magnetic phenomenon, the planning of a long-distance route or the study of a specific maritime sector.

The term “specialised chart” covers a wide range of documents. These may include thematic charts, regulatory charts, maritime zone charts, fisheries charts, magnetic variation charts, time-zone charts, polar charts, world charts and documents intended for specific professional activities.

The SHOM itself distinguishes nautical charts from “special charts” in its cartographic catalogue. This distinction illustrates the fact that maritime cartography is not limited to charts used directly for navigation.

What is a Specialised Chart?

A specialised chart is a cartographic representation whose content is selected and organised around a particular purpose.

A conventional nautical chart must provide the navigator with the information required to operate the vessel safely: depths, soundings, hazards, wrecks, aids to navigation, lights, landmarks, channels, anchorages and ports.

A specialised chart answers a different question.

It may, for example, be used to determine:

• which ocean route is most appropriate for a passage;

• how magnetic variation changes across a geographical area;

• which time zones are crossed;

• where maritime jurisdictional boundaries lie;

• how particular fishing areas are distributed;

• how polar regions are represented;

• how to determine an orthodromic route;

• what specific characteristics apply to a maritime area;

• which areas are subject to particular constraints or uses.

These documents are therefore generally complementary to nautical charts rather than intended to replace them.

Specialised Cartography as a Complement to Navigation

Long-distance passage planning often requires several levels of cartographic information.

For an Atlantic crossing between Le Havre or Brest and Fort-de-France, for example, a small-scale chart can provide an overview of the entire passage. Specialised charts can then provide additional information concerning routes, time zones, magnetic variation, meteorological areas or geographical characteristics of the ocean.

The same principle applies to a voyage between Marseille, Genoa and Athens in the Mediterranean, a passage across the Indian Ocean between Durban and Port Louis, or a trans-Pacific voyage between Panama, the Marquesas and Tahiti.

Specialised charts are therefore particularly useful when navigation extends beyond the immediate coastal environment.

SHOM Specialised Charts

SHOM distinguishes several families of charts and specialised documents in its catalogue. Its general catalogue includes nautical charts, chart assemblies and special charts.

The special-chart category includes, among other documents, world charts and polar charts, together with charts dealing with magnetic variation, time zones and the determination of orthodromic routes, distances and bearings.

These documents perfectly illustrate the purpose of specialised cartography: the chart is no longer intended solely to represent coastlines and navigational hazards, but to provide information adapted to a specific maritime operation.

Ocean Navigation Charts and Long-Distance Passages

Small-scale charts are particularly suitable for studying long distances.

They allow a large part of an ocean to be displayed on a single sheet and can be used to plan passages between continents.

For navigation in the North Atlantic, for example, they can be used to study routes between Europe and North America, with ports such as Brest, Southampton, Lisbon, Halifax, New York and Montréal.

In the South Atlantic, specialised cartography can be useful for planning passages between the Brazilian coast, southern Africa and the Atlantic island groups.

In the Indian Ocean, major routes linking Durban, Cape Town, Port Louis, Victoria in the Seychelles, Colombo and Singapore require a small-scale overview before being developed using larger-scale charts.

Polar Charts

Polar regions present specific cartographic challenges.

At high latitudes, certain map projections are better suited than the Mercator projection commonly used for many nautical charts. Distances, directions and the representation of meridians must be interpreted carefully.

A polar chart provides a representation adapted to the Arctic and Antarctic regions.

It can be used to study routes around Greenland, Iceland, the Svalbard archipelago, the Northwest Passage or Antarctic waters.

Polar charts are also useful for understanding major ocean routes, the geography of the polar regions and the relationships between continents and oceans.

Magnetic Variation Charts

Magnetic variation is the angular difference between geographic north and magnetic north.

This information is essential when using a magnetic compass or when converting a magnetic bearing into a true bearing.

Magnetic variation changes according to geographical position and also varies over time. A magnetic variation chart therefore provides a specialised representation of the Earth's magnetic field.

It can be particularly useful for offshore navigation, ocean passages and activities requiring a clear understanding of magnetic references.

It complements the information found on conventional nautical charts and helps the navigator understand the corrections required when using a magnetic compass.

Time-Zone Charts

A time-zone chart addresses a different but equally important issue during an ocean passage.

When a vessel crosses several time zones, local time changes progressively in relation to the reference time.

A world time-zone chart provides a visual representation of the theoretical boundaries between time zones and their organisation on a global scale.

It can be useful when planning an Atlantic, Pacific or Indian Ocean passage, particularly when organising watches, communications, port appointments or time management on board.

Orthodromic Charts and Long-Distance Route Planning

An orthodromic route is the shortest path between two points on a sphere or on an appropriate representation of the Earth.

Over very long distances, the difference between an orthodromic route and a loxodromic route can become significant.

A chart or plotting aid dedicated to orthodromic routes can therefore be used to study the distance, bearing and geometry of a long-distance passage.

This is particularly relevant to passages across the Atlantic, Pacific and Indian Oceans.

For a voyage between Brest and New York, Lisbon and Miami, Panama and Papeete, or Auckland and Cape Town, understanding the geometry of the Earth becomes essential when analysing the route before taking meteorological and navigational constraints into account.

Specialised Charts and Maritime Areas

Some specialised charts are designed to represent maritime boundaries and the use of maritime space.

SHOM, for example, produces Action de l'État en Mer charts at small scale showing the limits of maritime areas under French jurisdiction, administrative boundaries and certain zoning arrangements arising from international agreements. These documents may cover the Atlantic, the English Channel and North Sea, the Mediterranean and French overseas territories such as New Caledonia, Wallis and Futuna and French Polynesia.

These documents serve very different purposes from nautical charts intended for coastal navigation.

They may be relevant to administrations, maritime professionals, researchers, marine spatial planning specialists and users working with maritime boundaries and the use of ocean space.

Specialised Charts and Overseas Territories

Specialised cartography is particularly important for overseas territories.

The maritime areas of French Polynesia, New Caledonia, the French Caribbean, French Guiana, Réunion and the French Southern and Antarctic Lands have geographical and administrative characteristics very different from those of mainland France.

A specialised chart can provide an appropriate-scale overview of these territories, particularly when an EEZ or a large oceanic area needs to be represented.

In the South Pacific, for example, the distances between Tahiti, the Tuamotu Islands, the Marquesas and New Caledonia make a small-scale cartographic overview particularly useful.

Specialised Charts and Digital Cartography

Specialised cartographic requirements also exist in digital formats.

SHOM provides raster nautical charts in GeoTIFF format, georeferenced to WGS84 and projected in Mercator, as well as S-57 vector data for official electronic navigational charts. Vector charts represent individual cartographic objects such as buoys, wrecks, cables, regulated areas and soundings.

This distinction is important: a specialised digital chart is not necessarily an ENC intended for electronic navigation.

Depending on its format and purpose, it may be used within a charting application, GIS, route-planning software or a specific professional environment.

How to Choose a Specialised Chart

The choice primarily depends on the intended purpose.

Before using a specialised chart, it is useful to check:

• the geographical coverage;

• the scale;

• the cartographic projection;

• the subject represented;

• the date or edition of the document;

• the format, paper or digital;

• the geodetic reference system;

• the intended use;

• compatibility with the navigational charts being used;

• whether current regulatory information is also required.

Scale is particularly important. A chart covering the entire Atlantic will not provide the same level of detail as a coastal chart of the English Channel or a harbour plan.

Maritime Chart Publishers and Hydrographic Offices

Specialised charts form part of the broader range of major hydrographic offices and specialist maritime publishers.

SHOM is the French reference for official hydrographic charting of areas for which France has cartographic responsibility.

ADMIRALTY, published by the United Kingdom Hydrographic Office, also provides an extensive range of specialised charts and maritime publications covering British, European and many oceanic regions.

Other specialist publishers such as Imray and NV Charts can complement this documentation depending on the geographical area and intended use.

The value of a specialist maritime bookshop lies precisely in being able to distinguish between different types of charts: nautical charts, specialised charts, sedimentological charts, fisheries charts, routeing charts, polar charts and regulatory documents.

Practical Uses of Specialised Charts

A specialised chart can be used at several stages of a maritime project:

• planning an ocean passage;

• preliminary route analysis;

• planning polar navigation;

• analysing magnetic variation;

• organising time-zone changes;

• studying maritime boundaries;

• preparing navigation in an overseas territory;

• training for offshore navigation;

• geographical or scientific analysis;

• preparing professional maritime operations.

It can be consulted on its own for the thematic information it contains, but when actual navigation is involved it should generally be used together with the appropriate nautical documents.

Conclusion

Specialised charts are an essential part of professional maritime documentation. They address requirements that a conventional nautical chart cannot always cover: representation of maritime areas, magnetic variation, time zones, orthodromic routes, polar regions, major ocean passages or specific uses of maritime space.

Their value is particularly evident during offshore and ocean navigation, but also in professional, scientific, administrative and educational fields.

For an Atlantic crossing, a Pacific passage, a Mediterranean voyage or planning in polar regions, combining conventional nautical charts with specialised charts provides a more complete understanding of the maritime environment.

The “Specialised Charts” category at Nautic Way Maritime Bookshop therefore brings together dedicated cartographic documents intended to complement nautical documentation and meet specific technical requirements.

FAQ

What is a specialised chart?

A specialised chart is a cartographic document designed to represent specific maritime information. It may cover magnetic variation, time zones, orthodromic routes, maritime boundaries, polar regions, fisheries or other specialised subjects.

Does a specialised chart replace a nautical chart?

No. A specialised chart is generally complementary to a nautical chart. It provides thematic information that is not necessarily intended for direct navigation.

What is a specialised chart used for during an ocean passage?

It can be used to study additional information such as long-distance routes, orthodromic routes, time zones, magnetic variation or specific geographical characteristics of the ocean being crossed.

What is the difference between a nautical chart and a special chart?

A nautical chart is primarily designed to represent information required for navigation. A special or specialised chart is designed around a particular theme or purpose. SHOM explicitly distinguishes nautical charts from special charts in its catalogue.

Can a specialised chart be used in navigation software?

This depends on the format and design of the document. Some digital data are georeferenced and can be used in charting software or GIS, while S-57 ENCs comply with specific standards for electronic navigation.

What is a magnetic variation chart?

It is a chart representing the variation between geographic north and magnetic north. It can be used to study the magnetic corrections required when working with a magnetic compass.

What is a time-zone chart used for in navigation?

It provides a visual representation of the different time zones crossed during a passage and helps explain changes in local time during long ocean voyages.

Why use a polar chart?

Polar regions require cartographic representations adapted to high latitudes. A polar chart facilitates the study of geography, routes and distances in Arctic and Antarctic regions.

What is an orthodromic route?

An orthodromic route is the shortest path between two points on a sphere. It is particularly important for long-distance navigation across the Atlantic, Pacific and Indian Oceans.

Do specialised charts cover French overseas territories?

Yes. Some SHOM specialised charts cover French overseas territories including French Caribbean and Guiana, French Polynesia, New Caledonia, Wallis and Futuna and the southern Indian Ocean. They can, among other things, represent maritime areas and their boundaries.

Which organisations publish specialised maritime charts?

SHOM and ADMIRALTY – UKHO are two major references for official maritime cartography. Specialist publishers such as Imray and NV Charts also produce cartographic documents for particular regions and uses.

Why are specialised charts useful in a maritime bookshop?

They complement conventional nautical charts by providing specialised information. Planning a complex voyage may require several different types of documents in order to study the route, geography, maritime constraints and specific characteristics of the area.