Nautical chart symbology

Understanding the symbols and their meanings on nautical charts is as essential in navigation as it is to know the traffic rules for driving in the city. These are maps designed in scale in a specific way to make it safer. These representations show different details, in the form of symbols, such as the depth of the water, the type of ocean floor and its topography, the coast characteristics and the possible dangers that may appear at sea with their corresponding aids.


The scale and different types of nautical charts

One of the aspects to take into account when reading the symbology of a nautical chart is the scale. This defines the different types of existing charts:

  • Oceanic charts: With scales equal or inferior to 1:3 000 000. These are the most detailed ones:
  • Route charts: between 1:3 000 000 000 and 1:1 000 000.
  • Landfall charts: Between 1:1,000,000 and 1:300,000.
  • Coastal charts: between 1:300,000 and 1:100,000.
  • Quartermasters: Scales greater than 1:100,000. They are the ones with less detail, but cover more space.

All of them can complement each other and usually one or the other is used depending on the routes to be made and the different trajectories. A long trip is not the same as one that is limited to a smaller area. Another important detail to remember is to keep the nautical chart updated because underwater topography can change in a short time due to recurrent geological phenomena, such as erosion, landslides or underwater volcanic eruptions. All of these are more common than you might think.


Relevant aspects of a nautical chart

In addition to the scale, there are other key aspects relevant to the interpretation of a chart:

  • Detailed cartography including contour lines and data on the scale used.
  • Coastal lines with tidal data, location of breakwaters and bars, etc.
  • Topographic surveys of the underwater terrain known as bathymetry.
  • Possible obstacles on the seabed such as coral reefs, seamounts, etc.
  • Aids to navigation such as lighthouse locations.
  • Recommended navigation routes.
  • Offshore installations such as buoys and other structures.
  • Zones and limits at sea that serve to know the sectors that correspond to each country.
  • Port facilities and services, including marinas.
  • It can include aerial photos of the coasts to clarify some details that may not be well appreciated in the maps.
  • Drawings and diagrams of some relevant structures. This aspect may be more relevant in the case of marine research survey campaigns.

All these indicators are represented with a series of symbols explained in the following section.


Symbols used on nautical charts

All nautical chart symbols are drawn inside the map and explained in its legend. The different nautical abbreviations can be distributed in several different sections, which represent general aspects, topographic aspects, hydrographic aspects and navigational aids.

General Aspects

  • The chart numbering: This depends on its date, location, type of scale, etc. Generally, it is usually located on the upper right or left side.
  • Longitude and latitude in degrees: Written in pink. This data helps measure distances and calculate magnetic deviations in each case.
  • Indexes and abbreviation legends and legends, international abbreviations and general indexes of all the above in alphabetical form.

Topographic data

Topographic data provides information about the seabed in order to avoid accidents or for sampling or study in the case of research vessels. All this is represented by symbols whose concrete description is in the legend of the chart:

  • Natural seabed features: undulating shapes for reliefs, seamounts, etc.
  • Artificial features: Representative drawings for each structure.
  • Marks: Lighthouses, mining symbols, etc.
  • Ports: Depicted next to coastlines.
  • Topographic terms: Represented as lines.

the symbology on nautical charts

Hydrographic data

These are data related to the sea, currents, composition, etc. Not all of them are necessary for passenger ships, but they are necessary for research and fishing.

  • Tides and currents: Arrows, spirals, wavy lines, etc.
  • Depths: Contour lines with corresponding measurements.
  • Nature of the seabed: Presence of corals, mounts, etc., all with their symbols similar to those shown on other maps.
  • Rocks, wrecks and obstructions: Symbols are shown in the chart legend.
  • Offshore installations: Oilfields, cables, etc. Shown with dashed lines or squares.
  • Routes: Thick arrows and triangles.
  • Limits: Dots indicating the area from which, for example, you cannot fish, indicated by a crossed-out fish.

Navigational aids and other services

Although maps and compasses are very practical items, other navigational aids are also useful to visually enhance the data. This way, it is possible to know where to find them in case of need. Some of these services are reflected in the chart:

  • Lights: In the form of a spotlight indicating the direction of origin.
  • Buoys and beacons: Schematic drawings of these in the place where they are located.
  • Fog signals: Several lines together and degraded in size.
  • Radars, radio and satellite signals: circles and data with numbers and letters.
  • Other services: Assistance, among others. Its symbology depends on the service in question.
  • Small craft facilities: Flags, parking signs, etc.

Knowledge of the different symbols of nautical charts is basic for a safer navigation. Most of them also include wind roses, which are the well-known drawings of a compass indicating the north of the map.

In addition to all of the above, it is also important to note the year in which the chart was printed and data on the deviation in the magnetic field. This information helps positioning yourself correctly. To do this, a series of calculations must be carried out that will help calibrate the location devices, updating them on the go depending on where you are and the different normal variations of the Earth’s magnetic field. Without a correct location, a nautical chart is of little use.

In short, knowing and studying the symbols and their meanings on nautical charts contributes to safer navigation. Suisca Group offers everything a ship may need in its scale, such as this basic documentary resource.