nautical charts

A Description of Nautical Charts


Mariners rely on nautical charts to navigate. An effective use of a chart improves your navigation to your destination and prevents accidents. Frequently referencing a chart allows you to spot obstacles you might not otherwise notice. Your boat can be stopped in its wake by obstacles, such as rocks and sandbars, and could cause harm:

  1. you
  2. your boat
  3. the environment

Abbreviations, Symbols, and Terms

Chart 1 symbols, abbreviations, and terms are listed here.

Chart 1 Symbols, Abbreviations and Terms Used on Charts can be used to help you interpret your nautical chart from the Canadian Hydrographic Service (CHS). After the nautical charts, this publication is essential to have when you’re at sea.

The following chart lists all the symbols, abbreviations, and terms used on navigation charts published by the CHS. These symbols and abbreviations are used in our charts in hundreds. Our charts follow international specifications, allowing countries around the world to use them.

Title block

Graph title block example.

A nautical chart’s title block is the very first thing you should pay attention to. When looking at a chart, it’s often overlooked.

Regional identification

The regional identification of the title blocks indicates the general geographic area of the chart.

Main title

There is a specific geographic area specified in the title block of the chart.

Scale identification

The ratio between the size of the chart and the earth is referred to as ‘natural scale.’ For example, 1:15 000 means that 1 unit on the chart is equal to 15 000 units on the earth. A list of the different types and scales of charts you can use is given below.

  • Harbour charts are:
    • large scale, 1:2 001 to 1:20 000
    • The vessel is used to navigate through harbours and parts of the ocean where there are shoals
  • Approach charts are:
    • 1:20 001 to 1:50 000
    • A detailed approach to coasts can be made with this technique
  • Coastal charts are:
    • 1:50 001 to 1:150 000
    • used in fisheries charts
    • It showed continuous and extensive inshore coverage so sightings of landfall could be made
  • General charts:
    • are 1:150 001 to 1:500 000
    • used in fisheries charts
    • The coverage offshore goes beyond what is needed to make landfall easy to see inshore
  • Sailing charts are:
    • 1:500 001 and smaller
    • To navigate offshore without being able to see land

Projection identification

A chart projection involves representing curved surfaces (such as the earth) on flat pieces of paper (the chart).

Nautical charts are typically drawn using the Mercator projection. Flattening virtually eliminates shape distortions and direction distortions.

Depths note

Depths on the chart are indicated by the note in what units they are measured in. The depth is shown on charts as feet and fathoms (1 fathom is equal to 6 feet) or metres and centimetres.

At some point, all charts in Canada will show depth in metres.

Chart showing depths.

Elevations note

Describes the datum used in showing the elevation of structures and clearances for bridges and overhead cables. The note provides details on the clearance required to travel under bridges and over the overhead cables.

Horizontal datum

Chart with horizontal datum example.

It is used to position objects on Earth’s surface by providing a starting point. Symbols, abbreviations, and terms used on charts are listed in Chart 1 Symbols, Abbreviations, and Terms Used on Charts.

Classification diagram of sources

Identify where the data in the classification diagram came from and how old it is by including notes on the source.

Symbol reference note

Note that at the end of the title block there is a symbol reference note. Symbols & Abbreviations Used In Chart 1 is in this section.