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Canadian Chart 1 Symbols, Abbreviations and Terms

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Chart 1 contains the symbols, abbreviations and terms used on nautical charts published by the Canadian Hydrographic Service, which are based upon the Chart Specifications of the International Hydrographic Organization.

IHO REFERENCE NUMBER. The IHO has published a standard list of symbols, abbreviations and terms from a publication called INT 1 which Canada follows. It assigns a letter to each major category of charted features (such as “D” for cultural features) and a number to each symbol or abbreviation within a category.

LONGITUDES are referred to the Meridian of Greenwich.

BEARINGS on charts refer to the true compass and are measured from 000° clockwise to 359°.

CHART DATUM is the plane of reference for soundings and is stated in the title of each chart. Supplementary information may be given in a table, note or graph. Chart datum is the low water plane to which are referenced the depths of water over features permanently covered by the sea and the elevations of those features which are periodically covered and uncovered. Some low waters can be expected to fall below chart datum. This only occurs under certain astronomical conditions, but, where the range of tide is small, meteorological disturbances may cause even average tides to fall below chart datum. In tidal waters, the CHS uses the level of Lower Low Water, Large Tide or Lowest Normal Tide as its reference plane for chart datum. In non-tidal waters, a low water level is adopted as datum.

DEPTHS. The units used for soundings (metres, fathoms or feet) are stated in the title of the chart. On metric charts, the legend METRIC/MÉTRIQUE set in large type and printed in magenta is displayed in the border of the chart. Depths are expressed in the following ways on Canadian charts:

  1. Metres and Decimetres up to 21 metres and in Metres only in depths greater than 21 metres.
  2. Metres and Decimetres up to 30 metres and in Metres only in depths greater than 30 metres.
  3. Fathoms and Feet up to 11 fathoms and in Fathoms only in depths greater than 11 fathoms.
  4. Fathoms and fraction of fathoms on a few older charts.
  5. Feet.

On certain charts for use by deep-draught vessels and where the depth information is sufficiently precise, soundings between 21 metres (11 fathoms) and 31 metres (16 fathoms) may be expressed in metres and decimetres (fathoms and feet). The geographical position of a sounding is the centre of the depth figure.

DRYING HEIGHTS. Underlined figures on drying areas or in brackets against features are elevations above chart datum. Where the drying elevation figure cannot be placed in its exact position, it is placed close to it and enclosed in brackets.

ELEVATIONS AND VERTICAL CLEARANCES. On charts of tidal waters, elevations of lights, islands, etc., and vertical clearances under structures such as bridges and power lines are normally given above Higher High Water, Large Tide. On charts of non-tidal waters, elevations and vertical clearances are normally given above chart datum. The datum for elevations and clearances is always stated in the chart title. When an elevation figure cannot be placed on the feature, it is placed close to it and enclosed in brackets. On metric charts, the vertical clearance is given in metres and decimetres up to 10.0 metres and in whole metres thereafter. On non-metric charts, the vertical clearance is given in feet.

HORIZONTAL DATUM. The name and date of the horizontal datum used for a chart are shown in the title with a statement, where appropriate, about the corrections to be applied to the geographical positions to convert them to the international reference system of the internationally recognized regional datum.

SCALES. The natural scale is the ratio between a measurement on the chart and the actual distance on the surface of the earth. It is expressed with a numerator of 1 (e.g. 1:200 000).

INTERNATIONAL NAUTICAL MILE. The international nautical mile is equal to 1852 metres (6076.1 feet). For practical purposes, the NAUTICAL MILE is used for expressing distances. A sea mile is the length of one minute of arc, measured along the meridian, in the latitude of the position.

CHART COLOURS AND SYMBOLOGY. The colour presentation and size of symbology on Canadian charts is not always in accord with that shown in this publication. Lettering styles and capitalization vary considerably on charts published by the CHS and may not be exactly as shown in this publication; however, no change in meaning is implied by these differences.

LORAN-C. Charts that include a lattice overprinting are identified by the prefixes L(C), L/C or LC shown next to the chart number.

CHART REFERENCE. Where the limits or references to larger-scale charts are shown, they should normally be used as they contain further essential navigational information.

CHART EDITIONS. The three terms described below are used to indicate the publication status of Canadian charts.

NEW CHART. The first publication of a Canadian chart that covers an area not previously charted to the scale shown, or that covers an area different from any existing Canadian chart.

NEW EDITION. A new edition is a new issue of an existing chart that contains amendments essential to navigation in addition to those issued in Notices to Mariners. A new edition renders existing editions obsolete.

REPRINT. A reprint is a new print of the current edition of a chart that incorporates no amendments of navigational significance other than those previously promulgated in Notices to Mariners. It may also contain amendments from other sources provided that they are not essential to navigation. Previous printings of the current edition remain in force.

Chart 1 and Updates to Chart 1 are available online at no cost. As well, information concerning Canadian Nautical Charts, Sailing Directions, Tide Tables and other government publications of interest to mariners can be found at

The monthly edition of the Canadian Notices to Mariners is available online at This publication contains important general and safety information related to navigation, as well as corrections critical to navigation such as amendments to Canadian Charts; to the Radio Aids to Marine Navigation publication; and to the List of Lights, Buoys and Fog Signals publication.

The Notices to Mariners website offers a free email notification service whereby subscribers may be notified of updates concerning charts they select in their user profile. Subscribers may then choose to receive a weekly or monthly notification when a new Notice to Mariners affecting their charts is published.

In addition, subscribers may also choose to receive a notification when a new monthly edition of Notices to Mariners becomes available online. Users can subscribe to this service at the following website:

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