Types of nautical charts

Types of navigational charts

The charts used for navigation are the following:

Mercator projection

Used for loxodromic navigation. The Mercator projection is named after Mercado, who developed it. This maritime navigation chart is based on a cylinder, in which the meridians are shown as parallel and equidistant lines. The parallels also appear as straight lines, but in their case, the distance increases as they move away from the equator.

Gnomonic projection

This is an azimuthal projection whose point of perspective is the earth. It consists of great circles as straight lines, regardless of their orientation. This is a very useful projection for navigation, as the larger circles point to the shortest distance routes.

Classification of nautical charts according to their scale

According to their scale, there are also different types of navigational charts: general or oceanic charts, medium coastal charts, coastal charts, approaches charts and portolan charts. The characteristics of each of these are described here:

General Charts: Cover a great area of coastline and sea, mainly used in ocean navigation. Scale: 1/30,000,000 to 1/3,000,000.
Medium coastal charts: Used for medium-sized routes. Scale: 1/3,000,000 to 1/200,000.
Coastal navigation charts: Necessary for navigating by surveying the coastline. Scale: 1/200,000 to 1/50,000.
Approaches: For approaching harbours or avoiding accidents. Scale: 1/25,000.
Portolan charts: Scale less than 1/25,000. Detailed small areas of coastline and sea.
River charts: Scale 1/50,000 or higher. Used for navigable rivers; rarely for position determination.

Importance of nautical charts

Anyone who has ever been at the helm of a ship knows that this document is of vital importance. It is a map detailing water areas, lines and coastal ports. It also provides valuable information on the depth of the waters, restricted areas, recommended routes or obstructions.

The main purpose of the different types of nautical charts is to provide up-to-date information to avoid collisions, grounding or navigating in restricted areas. This allows both the vessel itself and other vessels to navigate safely.

Among the valuable information it contains, a few points can be highlighted:

Reticle
Magnetic variation
Terrestrial topography
Marks on land and sea
Main lines
Maritime radio, radionavigation and radiodetermination stations

For some time now, most navigators find it cumbersome to use a conventional chart and make calculations with instruments such as a compass, pencil or parallel rules. This is why electronic charts are increasingly being used.

Nowadays, both formats coexist. Vector or scanned charts are available in digital format. Choosing between paper or digital versions depends on several factors:

If a ship’s master has the appropriate local knowledge
Whether the ship is equipped with a proper electronic chart display system
How electronic information is used and displayed at the correct scale

Two types of electronic charts:

Raster Navigational Chart: Scanned image of a paper chart, reproduced based on official standards.
Electronic Navigational Chart: Created digitally by hydrographic services and fully official.

Charts must be published by a public organisation to be considered official. Any other chart is a commercial chart.

Raster or scanned charts are digital copies of official charts and are endorsed by governmental organisations. Electronic charts are created at the request of governmental institutions or hydrographic services.

In short, nautical charts are essential for navigation due to their precision. At Suisca, we are official distributors of Admiralty nautical charts in Spain, published by UKHO. With nautical charts, navigators gain precise knowledge of their area and improve safety, avoiding accidents.