Shom Nautical Charts – French Hydrographic and Oceanographic Service

Understanding Shom nautical charts and choosing the right document for your navigation

Shom, the French Hydrographic and Oceanographic Service, is France’s official hydrographic service and a reference for marine charting and nautical information. Shom nautical charts are used for coastal navigation, offshore navigation, harbour approaches, recreational boating, fishing, commercial shipping and route planning. Librairie Maritime Nautic Way offers the main families of Shom nautical charts, available in paper or digital format.

A Shom nautical chart provides a precise and structured representation of the marine environment: depths, soundings, depth contours, rocks, wrecks, shoals, buoys, lights, channels, anchorages, ports, currents and various regulatory limits. Choosing a Shom chart does not depend solely on the geographical area. Its scale, format, intended use and, for digital charts, compatibility with the software being used must also be considered.

Shom charts are particularly sought after for navigation along the French coastline, but some references also cover international areas, ocean crossings and more distant regions. The catalogue therefore makes it possible to search for a Shom nautical chart for the English Channel, Brittany, the Atlantic, the Mediterranean, the North Sea, the Indian Ocean, the Pacific, the Caribbean or more specific navigation areas.

What are the differences between Shom C, L, G, Z and Raster charts?

The five families of Shom documents meet different requirements. C and L charts are conventional nautical charts, while G and Z charts provide specialised information. Shom Raster, meanwhile, is a digital representation of a nautical chart.

Shom C nautical charts: the standard chart

The Shom C is the standard paper nautical chart. It is generally presented flat and rolled in a tube. Shom C charts are printed on 120 g/m² paper and are generally available in A0 format or smaller formats depending on the reference.

They are intended for a wide range of uses: coastal navigation, offshore navigation, passage planning, approaches to maritime areas and preparation for port calls.

A Shom C chart can, for example, be used to plan a voyage between Brest and Ushant, sail along the Brittany coast, prepare a Channel crossing or work on a route in the Mediterranean.

The level of detail naturally depends on the chart scale. A general chart allows the navigator to view a large maritime area, while a larger-scale chart is more suitable for coastal navigation or a harbour approach.

Shom L nautical charts: a chart folded to A4 size

The Shom L contains the cartographic information of the corresponding C chart, but is presented folded to A4 size. Once unfolded, it returns to a much larger chart format.

This presentation is particularly useful for sailors who want a nautical chart that is easy to transport and simpler to store on board.

The main difference between Shom C and Shom L therefore concerns presentation and packaging. The choice between the two may depend on onboard use, available storage space and the way in which the chart will be consulted during navigation planning.

Shom G charts: understanding seabed characteristics

The Shom G is a sedimentological chart. It provides additional information about the nature and distribution of seabed sediments.

Different types of seabed may be represented, including sand, gravel, stones and other seabed formations.

This information can be particularly useful for fishing, marine environmental studies, professional activities and understanding the underwater environment.

A Shom G should therefore not be considered simply as an alternative to a conventional nautical chart. It is a complementary document intended for situations where seabed characteristics are important.

Shom Z charts: exercise and firing areas

The Shom Z, also known as a Zonex chart, is a nautical chart featuring a specific overlay showing the boundaries and designations of exercise and firing areas used by maritime forces.

This information makes it easier to identify areas where specific activities take place and should be considered together with nautical information and Notices to Mariners.

The Shom Z also retains the essential information found on a nautical chart: soundings, hazards, aids to navigation, lights, coastlines, channels and other information required for navigation.

It is particularly relevant to sailors operating in areas where military or exercise activities need to be taken into account.

Shom Raster GeoTIFF nautical charts: digital cartography

Shom Raster is a digital version of Shom marine cartography. The charts are provided in GeoTIFF format and retain the graphical appearance, symbology and layout of the original chart.

Raster charts function as georeferenced digital images. They can therefore be used with certain compatible charting, navigation or GIS software.

When selecting a Shom Raster chart, several parameters should be considered: chart number, geographical area, scale, projection, file format and compatibility with the software being used.

The GeoTIFF format preserves the geographical information required to position the chart correctly within a digital environment. Shom Raster charts are generally provided at a resolution of 300 dpi.

Information shown on a Shom nautical chart

A Shom nautical chart contains a large amount of information required to understand a maritime area. Depending on the reference and scale, it may include:

• depths and soundings;

• depth contours and depth lines;

• rocks and shoals;

• wrecks;

• landmarks;

• buoys and other aids to navigation;

• lights and their characteristics;

• navigable channels;

• anchorages;

• ports and harbour facilities;

• currents;

• certain regulatory boundaries or special areas.

This information is organised according to Shom cartographic conventions, allowing the navigator to build a coherent representation of the navigation area.

Shom charts for major ports and maritime areas

Shom nautical charts can support many routes around the French coastline and in various areas covered by Shom cartographic production.

In the English Channel and Brittany, navigation may involve Brest, Saint-Malo, Cherbourg, Le Havre, Dieppe, Calais, Ushant or approaches to the Cotentin Peninsula.

Along the Atlantic coast, charts may be used around Lorient, Concarneau, La Rochelle, Royan, Bordeaux, Bayonne or in the approaches to the Bay of Biscay.

In the French Mediterranean, they cover areas including Marseille, Toulon, Hyères, Cannes, Nice, Ajaccio, Bastia and the various approaches to Corsica.

For longer-distance navigation, certain Shom charts also cover areas of the Atlantic, Mediterranean, Red Sea, Indian Ocean, Pacific and other international navigation areas. The catalogue includes references for areas such as the Panama Canal, the South Atlantic and navigation zones around Cape Horn.

How to choose a Shom nautical chart

Choosing a Shom chart should be done in several stages:

• Identify the navigation area: French coast, English Channel, Atlantic, Mediterranean, overseas territory or international area.

• Determine the required scale: general, offshore, coastal or harbour.

• Choose the chart type: C, L, G, Z or Raster according to the intended use.

• Check the Shom chart reference corresponding to the area.

• For a digital chart, check compatible software and the technical specifications.

• Check the edition date and corrections before use.

For a complete voyage, several charts may be required. A general chart can be used to plan the overall route, while larger-scale charts can then be used for coastal approaches, channels, anchorages and ports.

Paper Shom charts and digital navigation

The development of chartplotters, navigation software and electronic systems has not eliminated the usefulness of paper nautical charts. They remain particularly useful for route planning, quickly understanding the geography of an area and maintaining an overall view of the voyage.

A paper chart can also complement digital cartography. The navigator then has two different forms of representation: the traditional paper chart and digital cartography.

Shom Raster meets the needs of users who wish to access Shom cartographic representation within a compatible digital environment.

Conclusion

Shom nautical charts provide cartographic documentation suitable for a wide range of uses, from coastal navigation to offshore passage planning.

The Shom C is the standard paper nautical chart, generally supplied rolled. The Shom L contains the information of the corresponding chart in a folded format that is easier to store. The Shom G provides specific information about seabed characteristics. The Shom Z incorporates specific information concerning exercise and firing areas. Finally, the Shom Raster GeoTIFF brings Shom cartographic representation into a compatible digital environment.

The choice therefore mainly depends on the navigation area, the required scale, the level of detail needed, the desired format and the intended use. This distinction makes it easier to select a Shom nautical chart suited to navigation in Brittany, the English Channel, along the Atlantic coast, in the Mediterranean or in other areas covered by Shom cartographic production.

FAQ – Shom Nautical Charts

What is Shom?

Shom, the French Hydrographic and Oceanographic Service, is France’s hydrographic service and is responsible, among other things, for producing and distributing nautical and hydrographic information and documents.

What is the difference between a Shom C and a Shom L chart?

The Shom C is a paper chart presented flat and generally supplied rolled. The Shom L is folded to A4 size and contains the cartographic information of the corresponding C chart.

What is a Shom G chart used for?

The Shom G is a sedimentological chart providing information about the nature and distribution of seabed sediments. It is particularly useful for fishing and studying the marine environment.

What is a Shom Z chart used for?

The Shom Z, or Zonex chart, contains an overlay showing the boundaries and designations of exercise and firing areas used by maritime forces.

What is a Shom Raster nautical chart?

It is a digital version of a Shom nautical chart, generally supplied in GeoTIFF format. It retains the graphical representation of the chart and can be used with certain compatible navigation, charting or GIS software.

Is a Shom Raster chart a vector chart?

No. Raster is a representation in the form of a georeferenced digital image. It differs from vector cartography, in which individual cartographic objects are stored as separate digital data.

Which Shom chart should I choose for sailing in Brittany?

The choice depends on the exact area, scale and type of navigation. A general chart may be suitable for route planning, while a larger-scale chart is generally required for coastal navigation or a harbour approach.

Which Shom chart should I use for a harbour approach?

A large-scale chart appropriate to the area generally provides more detailed information about depths, aids to navigation, channels, hazards and harbour facilities.

Do Shom charts only cover metropolitan France?

No. The Shom catalogue also includes charts covering various overseas territories and international areas, as well as passage charts and charts covering large ocean areas.

Why is scale important on a Shom nautical chart?

Scale determines the area represented and the level of detail available. A general chart covers a large area, while a large-scale chart represents a smaller area with greater detail.

Can a Shom paper chart be used with a GPS chartplotter?

Yes. A paper chart can complement electronic navigation and can be used to plan a route, check a position or maintain an overall view of the navigation area.

How do I choose between a paper Shom chart and a Shom Raster chart?

The choice mainly depends on the navigation method and equipment being used. A paper chart provides direct, overall consultation, while Raster is intended for a compatible digital environment.

Which French ports can be covered by Shom charts?

Depending on the references and areas covered, charts may include Brest, Saint-Malo, Cherbourg, Le Havre, Dieppe, Calais, Lorient, Concarneau, La Rochelle, Bordeaux, Marseille, Toulon, Cannes, Nice, Ajaccio or Bastia.