ISO 19018:2020

INTERNATIONAL ISO
STANDARD 19018
Second edition
2020-08
Ships and marine technology —
Terms, abbreviations, graphical
symbols and concepts on navigation
Navires et technologie maritime — Termes, abréviations, symboles
graphiques et concepts relatifs à la navigation
Reference number
ISO 19018:2020(E)
©
ISO 2020

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ISO 19018:2020(E)

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© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 19018:2020(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Special units in maritime navigation . 1
5 Reference directions. 2
5.1 North directions . 2
5.2 Dead ahead direction . 2
6 Course, heading, track, speed . 2
6.1 Course, heading . 2
6.2 Track . 4
6.3 Speed . 4
7 Bearings . 4
8 Corrections . 5
9 Influence of wind and current . 6
9.1 Wind . 6
9.2 Leeway and drift triangle . 6
10 Geographical coordinates, positions and lines, and graphical symbols .8
10.1 Geographical coordinates . 8
10.2 Positions and lines . 9
10.3 Graphical symbols .10
11 Waypoint navigation .10
12 Terms of time .11
12.1 Universal terms of time .11
12.2 Terms concerning time for navigation use .12
13 Astronomical navigation .13
13.1 Celestial coordinates, points, lines and angles on the celestial sphere .13
13.2 Great and small circles .13
13.3 Altitudes and angular distances on the celestial sphere .14
13.4 Sight reduction .15
13.5 Symbols of celestial bodies and sextant altitudes .16
14 Depth of water and tides .16
15 Terrestrial magnetism .18
16 Global Navigation Satellite System (GNSS) .19
16.1 Dilution of precision .19
Bibliography .20
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ISO 19018:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 8, Ships and marine technology,
Subcommittee SC 6, Navigation and ship operations.
This second edition cancels and replaces the first edition (ISO 19018:2004), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— Clause 2: updated referenced documents: ISO 31 deleted (its current revision, ISO 80000-3:2019,
does no longer mention the nautical mile, knot, degree and minute), and changed from IEC 60872
and IEC 60936 to related original IMO resolutions;
— added Clause 3, “Terms and definitions”, and subsequent clauses renumbered;
— items 4.1.1 to 4.1.3: referenced document changed from “ISO 31-1 and/or Chart INT 1” to “Chart INT”
only, as applicable;
— items 6.1 and 6.1.1: abbreviation of “course” changed from “CSE” to “CRS”, and the second sentence
of the explanation of 6.1 deleted (harmonized with that in radar navigation; IEC 62288 and/or
IEC 62388);
— items 6.1.1 to 6.1.15 and 7.1 to 7.5: updated “Definition, remarks” based on IMO Resolution MSC. 192
(79) (harmonized with abbreviation and definition in IEC 62288 and/or IEC 62388);
— items 6.1.1, 6.1.2 and 6.1.4: added 6.1.1 “course”, 6.1.2 “heading” and 6.1.4 “course to steer"
(harmonized with abbreviation and definition in IEC 62288 and/or IEC 62388);
— items 7.1 to 7.5: changed the "Definition, remarks", based on IMO Resolution MSC, 192[79];
— deleted former Clause 15, “Radar navigation”, and former Clause 16, “LORAN-C”; and former
Clause 17 renumbered as new Clause 16;
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ISO 19018:2020(E)

— new Clause 16 (former Clause 17): title changed from “Global Positioning System (GPS)” to “Global
Navigation Satellite System (GNSS)”;
— Bibliography: added “[4] IEC 62288:2014”, “[5] IEC 62388:2013”, "[6] IMO Resolution MSC. 191(79)"
and "[7] IMO Resolution MSC. 192(79)".
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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INTERNATIONAL STANDARD ISO 19018:2020(E)
Ships and marine technology — Terms, abbreviations,
graphical symbols and concepts on navigation
1 Scope
This document provides terms, abbreviations and graphical symbols for use in maritime navigation on
board ships. Symbols for use in mathematical formulae are also given, as applicable.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
Terms, abbreviation and symbols used in navigation are given in Clauses 4 to 16. Abbreviations can
prove useful, but they should not be used in mathematical formulae.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
navigation
process of finding the position of a craft or vehicle, and of planning, recording and controlling its
movement from one place to another
4 Special units in maritime navigation
Item International
Name of the unit Definition, conversion factors and remarks
No. symbol
4.1 Unit of length
4.1.1 nautical mile NM 1 NM = 1 852 m.
in charts: The nautical mile is not an SI-unit. This definition
a
M was adopted by the First International
Hydrographic Conference in 1929.
4.1.2 cable, cable length cbl One-tenth of a nautical mile. The cable is not an
SI unit.
a
Symbol M is to be used in Charts according to the “Chart Specifications of the IHO” which came into force at the XIIth
International Hydrographic Conference 1982 in Monaco.
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ISO 19018:2020(E)

Item International
Name of the unit Definition, conversion factors and remarks
No. symbol
4.2 Unit of velocity and speed
4.2.1 knot, knots kn
NM
11kn==0,/514 444ms
h
(see Chart INT 1).
Velocity is a vector quantity, whereas speed is
a scalar having magnitude only.
The knot is not an SI unit.
4.3 Unit of angle
4.3.1 degree °
π
1°= rad
180
4.3.2 minute '
1°
1'=
60
In maritime navigation, angles should be specified
in degrees, minutes and decimals of minutes
(example: write 17° 40,25' not 17° 40' 15").
Degrees and minutes are not SI units.
a
Symbol M is to be used in Charts according to the “Chart Specifications of the IHO” which came into force at the XIIth
International Hydrographic Conference 1982 in Monaco.
5 Reference directions
5.1 North directions
North directions are horizontal reference directions.
Item No. Term Abbreviation Definition, remarks
5.1.1 true north TN Northerly direction of the meridian (see 10.1.12).
5.1.2 magnetic north MN Northerly direction of the horizontal component
of the Earth's magnetic field (see 15.2).
5.1.3 compass north CN Northerly direction of the needle or zero-index of
a magnetic compass.
5.1.4 gyro north GyN Northerly direction indicated by the gyro-compass.
5.2 Dead ahead direction
Dead ahead direction is the direction ahead of the ship's fore-and-aft line.
6 Course, heading, track, speed
6.1 Course, heading
Course (CRS) and heading (HDG) are angles, measured in the horizontal plane from one of the reference
directions specified in Clause 5, counted clockwise from 000° through <360°, written as three-digit
numbers.
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ISO 19018:2020(E)

Item No. Term Abbreviation Definition, remarks
6.1.1 course CRS Direction of motion relative to ground or to sea,
of a ship, expressed as an angular displacement
from north.
6.1.2 heading HDG Direction in which the bow of a ship is pointing,
expressed as an angular displacement from north.
[SOURCE: IMO Resolution MSC. 192(79),
Appendix 2.]
6.1.3 true course TC Direction of motion relative to ground or to sea,
T CRS of a target, expressed as an angular displacement
from true north.
[SOURCE: IMO Resolution MSC. 192(79),
Appendix 2.]
6.1.4 course to steer CTS The direction in which the ship is intended to be
steered, defined as an angular displacement from
true course.
6.1.5 true heading TH Horizontal direction that the bow of a ship is
T HDG pointing, expressed as an angular displacement
from true north.
6.1.6 magnetic course MC Direction of motion relative to ground or to sea,
M CRS of a ship, expressed as an angular displacement
from magnetic north.
6.1.7 magnetic heading MH Horizontal direction that the bow of a ship is
M HDG pointing, expressed as an angular displacement
from magnetic north.
6.1.8 compass course CC Direction of motion relative to ground or to sea,
C CRS of a ship, expressed as an angular displacement
from compass north.
6.1.9 compass heading CH Horizontal direction that the bow of a ship is
C HDG pointing, expressed as an angular displacement
from compass north.
6.1.10 gyro course GyC Direction of motion relative to ground or to sea,
Gy CRS of a ship, expressed as an angular displacement
from gyro north.
6.1.11 gyro heading GyH Horizontal direction that the bow of a ship is
GY HDG pointing, expressed as an angular displacement
from gyro north.
6.1.12 course through water CTW Direction of the ship's movement through the
water, defined by the angle between the meridian
through its position and the direction of the ship's
movement through the water, expressed in angular
units from true north.
[SOURCE: IMO Resolution MSC. 192(79),
Appendix 2.]
6.1.13 course of advance, COA Direction from the ship's last fix (see 10.2.5) to the
course to make good next estimated position (see 10.2.3), expressed
in angular units from true north.
6.1.14 course over ground COG Direction of the ship's movement relative to the
Earth, measured on board the ship, expressed
in angular units from true north.
[SOURCE: IMO Resolution MSC. 192(79),
Appendix 2.]
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ISO 19018:2020(E)

Item No. Term Abbreviation Definition, remarks
6.1.15 course made good CMG Rhumb-line direction (see 10.2.11) between two
fixes (see 10.2.5).
6.2 Track
The term “track” is used
a) as the path of voyage over the ground (ground track) or through the water (water track), as plotted
in the chart, expressed in angular units from true north (000°) clockwise through <360°; one must
distinguish rhumb-line track (see 10.2.11) and great-circle track (see 10.2.9),
b) as the path of radar-targets on a plan position indicator.
Item No. Term Abbreviation Definition, remarks
6.2.1 intended water track WT Intended path of the ship's movement through
the water.
6.2.2 water track WAT TRK Actual path of the ship's movement through
the water.
6.2.3 intended ground track GT Intended path of the ship's movement over
the ground.
6.2.4 ground track GND TRK Actual path of the ship's movement relative
to the Earth.
6.2.5 track made good TMG Track between two fixes (see 10.2.5).
6.3 Speed
Item No. Name of the term Abbreviation Definition, remarks
6.3.1 speed SPD Own ship's speed in dead ahead direction (see 5.2)
produced by machine or sail.
6.3.2 speed through the water STW Speed of the ship relative to the water surface.
6.3.3 speed of advance, SOA Estimated speed of the ship relative to the Earth.
speed to make good
6.3.4 speed over the ground SOG Speed of the ship relative to the Earth, measured
on board the ship.
6.3.5 speed made good SMG Speed of the ship between two fixes.
7 Bearings
Bearing (BRG) is an angle measured in the horizontal plane from one of the reference directions
specified in Clause 5, measured clockwise from 000° through 360°, written as three-digit numbers. In
radar navigation, the abbreviation BRG for bearing is preferred.
Item No. Term Abbreviation Definition, remarks
7.1 true bearing TB Direction of a target from own ship’s consistent
T BRG common reference point (CCRP) or from another
target’s position, expressed as an angular
displacement from true north.
[SOURCE: IMO Resolution MSC. 192(79),
Appendix 2, modified – added CCRP.]
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ISO 19018:2020(E)

Item No. Term Abbreviation Definition, remarks
7.2 magnetic bearing MB Direction of a target from own ship’s consistent
common reference point (CCRP) or from another
target’s position, expressed as an angular
displacement from magnetic north.
[SOURCE: IMO Resolution MSC. 192(79),
Appendix 2, modified – added CCRP.]
7.3 compass bearing CB Direction of a target from own ship’s consistent
common reference point (CCRP) or from another
target’s position, expressed as an angular
displacement from compass north.
[SOURCE: IMO Resolution MSC. 192(79),
Appendix 2, modified – added CCRP.]
7.4 gyro bearing GyB Direction of a target from own ship’s consistent
Gy BRG common reference point (CCRP) or from another
target’s position, expressed as an angular
displacement from gyro north.
[SOURCE: IMO Resolution MSC. 192(79),
Appendix 2, modified – added CCRP.]
7.5 relative bearing RB Direction of a target’s position from own ship’s
R BRG consistent common reference point (CCRP)
expressed as an angular displacement from own
ship’s heading.
[SOURCE: IMO Resolution MSC. 192(79),
Appendix 2, modified – added CCRP.]
8 Corrections
The numerical value of a correction is the best estimate which can be made of the difference between
the true and the measured value of a parameter. The sign is such that a correction which is to be added
to an observed reading is taken as positive.
Item No. Name of the term Abbreviation Definition, remarks
8.1 magnetic variation MAG VAR Angle between the geographic and the magnetic
meridians (see 10.1.12 and 15.4) at any place of
the Earth, also called magnetic declination, from true
north to magnetic north, eastwards named E (sign
plus), westwards named W (sign minus).
8.2 deviation DEV Angle between the magnetic meridian (see 15.4)
and the axis of a compass card, expressed in degrees
east or west to indicate the direction in which
the northern end of the compass card is offset
from magnetic north when it is disturbed by local
attraction, from magnetic north to compass north,
eastwards named E (sign plus), westwards named W
(sign minus).
8.3 total compass error CE Sum of variation and deviation. Angle between true
correction north and compass north, from true north eastwards
named E (sign plus), westwards named W (sign
minus).
a
8.4 speed error correction δ Correction of the gyro heading error, which depends
Gy
on position, speed and course of the ship; sign plus
when the ship moves southwards, sign minus when
the ship moves northwards.
a
Formula symbol.
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ISO 19018:2020(E)

Item No. Name of the term Abbreviation Definition, remarks
8.5 gyro error correction GyE Correction of all errors (including speed error) of
a gyro compass. Angle between true north and gyro
north, from true north eastwards with sign plus,
error low, westwards with sign minus, error high.
8.6 gyro-R Correction of the measured error of a gyro compass
indication without speed error (gyro residual
aberration).
8.7 gyro-A Correction of the constant part of gyro-R; mean
value of measured gyro-R values.
8.8 leeway angle Angular difference between the course through
water and the course to steer (CTW − TC).
8.9 drift angle Angular difference between the course of advance
or course over ground and the course through water
(COA − CTW or COG − CTW).
8.10 leeway and drift angle Angular difference between the course of advance
or course over ground and the course to steer
(COA − TC or COG − TC); sum of leeway angle and
drift angle.
a
8.11 conversion angle u Angular difference at a point between the rhumb line
and a great circle (see 10.2.11 and 10.2.9) from that
point to another point on the Earth's surface.
a
Formula symbol.
9 Influence of wind and current
9.1 Wind
Wind direction is the direction where the movement of the air comes from. The vector of this movement
is in the opposite direction of the wind direction. For instance, in the case of an east wind, the movement
of the air is in the direction of 270° (direction of the vector in weather charts).
Item No. Name of the term Definition, remarks
9.1.1 true wind Velocity of the air (speed and direction) relative to a fixed point
on the Earth.
9.1.2 speed wind Velocity of the air (speed and direction) only caused by the
ship's motion relative to the Earth; (direction against course
over ground).
9.1.3 apparent wind, Velocity of the air (speed and direction) relative to the moving
relative wind ship; the vector of apparent wind or relative wind (wind feeling
on board) minus the vector of speed wind is equal to the vector
of true wind.
9.2 Leeway and drift triangle
See Figure 1.
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ISO 19018:2020(E)

Key
⊕ last fix (see 10.2.5)
1 leeway angle (see 8.8)
2 drift angle (see 8.9)
3 own ship's velocity (see 9.2.1)
4 intended water track (see 6.2.1 and 9.2.3)
5 intended ground track (see 6.2.3 and 9.2.5)
6 leeway vector (see 9.2.2)
7 drift vector (see 9.2.4)
DR dead reckoning position (see 10.2.1)
DR corrected dead reckoning position (sea position) (see 10.2.2)
cor
EP estimated position (see 10.2.3)
Figure 1 — Leeway and drift triangle
Item Definition of Item Magnitude Abbre- Item Direction Abbre-
Term
No. the vector No. of vector viation No. of vector viation
9.2.1 own ship's own ship's 9.2.1.1 speed (6.3.1) SPD 9.2.1.2 course to steer CTS
velocity velocity (6.1.4) TC
9.2.2 leeway vector ship's velocity 9.2.2.1 leeway drift 9.2.2.2 leeway set
due to influence
of wind
9.2.3 intended water ship's velocity 9.2.3.1 speed through STW 9.2.3.2 course through CTW
track relative to the water (6.3.2) water (6.1.12)
water
9.2.4 drift vector horizontal 9.2.4.1 drift 9.2.4.2 set
velocity of the
water surface
9.2.5 intended ship's velocity 9.2.5.1 speed of SOA 9.2.5.2 course of COA
ground track relative to the advance advance (6.1.13)
Earth (6.3.3)
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ISO 19018:2020(E)

10 Geographical coordinates, positions and lines, and graphical symbols
10.1 Geographical coordinates
Item No. Term Abbreviation Definition, remarks
10.1.1 geodetic datum A set of parameters specifying the reference co-
ordinate system used for geodetic control in the
calculation of coordinates of points on the Earth.
10.1.2 World Geodetic System WGS A global geodetic reference system developed by
the USA for satellite position fixing and recom-
mended by the IHO for hydrographic and car-
tographic use.
10.1.3 latitude, φ Angular distance from the Equator (00°) measured
geographic latitude LAT northwards or southwards through 90° and labelled
N or S to indicate the direction of measurement.
10.1.4 longitude, λ Angle at the Pole between the prime meridian
geographic longitude LON (000°) (see 10.1.13) and the meridian of a point on
the Earth, measured eastwards or westwards from
the prime meridian through 180° and labelled E or
a
W to indicate the direction of measurement .
10.1.5 geodetic latitude Angular distance between the plane of the
geodetic equator and the normal to a station on
the Earth ellipsoid, measured from the Equator
(00°) northwards or southwards through 90° and
labelled N or S.
10.1.6 geodetic longitude Angle between the plane of the geodetic prime
meridian (000°) and the plane of the station's
geodetic meridian, measured eastwards or west-
wards from the prime meridian through 180° and
a
labelled E or W .
10.1.7 geocentric latitude Angle at the centre of the reference ellipsoid
between the plane of the Equator (10.2.8) and the
radius vector to a point on the ellipsoid, measured
from the Equator (00°) northwards or southwards
through 90° and labelled N or S.
10.1.8 geocentric longitude Angle between the plane of the geocentric prime
meridian (000°) and the plane of the station's geo-
centric meridian, measured eastwards or west-
wards from the prime meridian through 180° and
a
labelled E or W .
10.1.9 astronomical latitude Angular distance between the plane of the celestial
equator (00°) and the plumb line through the
station, measured northwards or southwards
through 90° and labelled N or S.
10.1.10 astronomical longitude Angle between the plane of the prime meridian
and the plane of the station's celestial meridian
(see 13.2.8), measured eastwards or westwards,
from the prime meridian through 180° and la-
belled E or W.
10.1.11 parallel of latitude A small circle on the Earth's surface parallel to the
Equator.
10.1.12 meridian Great circle between the geographical poles of the
Earth; north-south-reference line.
10.1.13 prime meridian, The reference meridian 000°; origin for measure-
Greenwich meridian ment of longitude.
a
The planes of geographic, geodetic and geocentric meridians are identical.
b
Formula symbol.
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ISO 19018:2020(E)

Item No. Term Abbreviation Definition, remarks
10.1.14 difference of latitude d.lat The shorter arc o
...