lesson 02: terrestrial coordinate system/ chart projections and numbering learning...

LESSON 02:LESSON 02:Terrestrial Coordinate System/ Terrestrial Coordinate System/

Chart Projections and Chart Projections and NumberingNumbering

• Learning Objectives:Learning Objectives:

– Comprehend the terrestrial coordinate Comprehend the terrestrial coordinate systemsystem

– Comprehend the location of positions on the Comprehend the location of positions on the earth using latitude and longitudeearth using latitude and longitude

– Comprehend the basic properties of the Comprehend the basic properties of the most commonly used chart projectionsmost commonly used chart projections

Terrestrial Coordinate Terrestrial Coordinate SystemSystem

• The earth is an oblate spheroid, but The earth is an oblate spheroid, but for navigational purposes it is for navigational purposes it is considered a perfect sphere with a considered a perfect sphere with a circumference of 21,600 NM.circumference of 21,600 NM.

• On a perfect sphere at rest, all points On a perfect sphere at rest, all points on the surface are similar; reference on the surface are similar; reference points must be designated in order points must be designated in order to make any type of measurements.to make any type of measurements.


• When rotation is introduced, the spin When rotation is introduced, the spin axis introduces two reference points, axis introduces two reference points, the north and south poles.the north and south poles.

• The spin axis of the earth, together The spin axis of the earth, together with its poles, constitutes the basic with its poles, constitutes the basic reference points on which the reference points on which the terrestrial coordinate system is terrestrial coordinate system is based.based.


• Great Circle: the intersection of a plane Great Circle: the intersection of a plane passing through two points on the surface passing through two points on the surface of the earth and the center of the earth.of the earth and the center of the earth.

• Some key points:Some key points:– A great circle is the largest circle that can be A great circle is the largest circle that can be

drawn on the face of the earth.drawn on the face of the earth.– A great circle represents the shortest A great circle represents the shortest

distance between two points on the surface of distance between two points on the surface of the earththe earth..


• EquatorEquator

• MeridianMeridian


• Small Circle- any circle not passing through the center of the Small Circle- any circle not passing through the center of the earth.earth.


• Meridians of longitude are great circlesMeridians of longitude are great circles• Parallels of latitude are small circles Parallels of latitude are small circles

(with the exception of the equator)(with the exception of the equator)

Latitude and LongitudeLatitude and Longitude

• The equator divides the earth into the The equator divides the earth into the northern and southern hemispheres and northern and southern hemispheres and is the reference for parallels of latitude.is the reference for parallels of latitude.

• The prime meridian passes through the The prime meridian passes through the original position of the Royal Greenwich original position of the Royal Greenwich Observatory. It serves as the reference Observatory. It serves as the reference for meridians of longitude.for meridians of longitude.

Latitude and LongitudeLatitude and Longitude

• Meridians are divided in half:Meridians are divided in half:– upper branchupper branch– lower branchlower branch

• Prime MeridianPrime Meridian– upper branch is known as the upper branch is known as the

Greenwich meridianGreenwich meridian– lower branch is the 180th meridianlower branch is the 180th meridian

Longitude DefinedLongitude Defined

• The angular distance between The angular distance between the Greenwich meridian and the the Greenwich meridian and the meridian passing through a meridian passing through a particular point on the earth’s particular point on the earth’s surface. Longitude is measured surface. Longitude is measured in degrees of arc from 0 to 180 in degrees of arc from 0 to 180 degrees, either east or west.degrees, either east or west.

Latitude DefinedLatitude Defined

• The angular distance between The angular distance between the Equator and the parallel the Equator and the parallel passing through a particular passing through a particular point on the earth’s surface. point on the earth’s surface. Latitude is measured in degrees Latitude is measured in degrees of arc from 0 to 90 degrees, of arc from 0 to 90 degrees, either north or south.either north or south.

LongitudeLongitude

LatitudeLatitude

Measurement of DistanceMeasurement of Distance

• Since latitude lines are parallel, the Since latitude lines are parallel, the length of one degree of latitude is the length of one degree of latitude is the same everywhere on earth (60 NM).same everywhere on earth (60 NM).

• As the distance from the equator As the distance from the equator increases, the length in miles of one increases, the length in miles of one degree of longitude decreases, so degree of longitude decreases, so NEVER use the longitude scale to NEVER use the longitude scale to determine distances on a chart. determine distances on a chart.

Measurement of DistanceMeasurement of Distance

Chart ProjectionsChart Projections

• Desirable qualities of a chart projection:Desirable qualities of a chart projection:– Correct angular relationshipsCorrect angular relationships– Representation of areas in their correct proportions Representation of areas in their correct proportions

relative to one anotherrelative to one another– True scaleTrue scale– Rhumb lines represented as straight lines.Rhumb lines represented as straight lines.

Note: Note: Rhumb lines are lines on the surface of the Rhumb lines are lines on the surface of the earth that cross all meridians at the same angle. earth that cross all meridians at the same angle. Ships on a constant course follow rhumb lines.Ships on a constant course follow rhumb lines.

– Great circles represented as straight linesGreat circles represented as straight lines

Mercator ProjectionMercator Projection

• Imagine a cylinder rolled around the Imagine a cylinder rolled around the earth, tangent at the equator, and earth, tangent at the equator, and parallel to the earth’s axis.parallel to the earth’s axis.

• Meridians appear as straight vertical Meridians appear as straight vertical lines when projected outward onto lines when projected outward onto the cylinder.the cylinder.

Mercator ProjectionMercator Projection

Mercator ProjectionMercator ProjectionAdvantagesAdvantages

• Position, Distance, Position, Distance, and direction easily and direction easily determined.determined.

• True shape of True shape of features is features is maintained for small maintained for small areas (conformality)areas (conformality)

• Rhumb lines plot as Rhumb lines plot as straight lines.straight lines.

DisadvantagesDisadvantages• Distortion of true Distortion of true

size of surface size of surface features increases features increases with distance from with distance from the equator.the equator.

• Great circles Great circles appear as curved appear as curved lines.lines.

Gnomonic ProjectionGnomonic Projection• Surface features and reference lines on Surface features and reference lines on

the earth’s surface are projected outward the earth’s surface are projected outward from the center of the earth onto a tangent from the center of the earth onto a tangent plane.plane.

• Three basic types, depending on point of Three basic types, depending on point of tangency:tangency:– equatorial gnomonic (tangent at equator)equatorial gnomonic (tangent at equator)– polar gnomonic (tangent at either pole)polar gnomonic (tangent at either pole)– oblique gnomonic (tangent somewhere else)oblique gnomonic (tangent somewhere else)

Gnomonic ProjectionGnomonic Projection

Gnomonic ProjectionGnomonic ProjectionAdvantagesAdvantages

• Great circles appear Great circles appear as straight lines as straight lines (shortest distance (shortest distance between two points)between two points)

• Tolerable distortion Tolerable distortion within 1000 miles of within 1000 miles of the point of the point of tangencytangency

DisadvantagesDisadvantages• Rhumb lines appear Rhumb lines appear

as curved linesas curved lines• Distance and Distance and

direction cannot be direction cannot be measured directlymeasured directly

• Not conformal (true Not conformal (true shapes are not shapes are not presented)presented)

Gnomonic ProjectionGnomonic Projection

Gnomonic vs. MercatorGnomonic vs. Mercator

GnomonicGnomonic• Since great circles Since great circles

appear as straight appear as straight lines, used to lines, used to determine the determine the shortest route shortest route between two points. between two points. This information is This information is then transferred to a then transferred to a Mercator chart.Mercator chart.

MercatorMercator• Used for everyday Used for everyday

navigation, due to navigation, due to the ease of the ease of measurement of measurement of position, distance, position, distance, and direction.and direction.

Gnomonic vs. MercatorGnomonic vs. Mercator

Nautical ChartsNautical Charts

• Two government activities are Two government activities are responsible for producing charts:responsible for producing charts:

• Defense Mapping Agency (DMA)Defense Mapping Agency (DMA)– ocean areas of the world outside U.S. ocean areas of the world outside U.S.

territorial watersterritorial waters

• National Ocean Service (NOS)National Ocean Service (NOS)– inland and coastal waters of the U.S. inland and coastal waters of the U.S.

and its possessionsand its possessions

Chart Numbering SystemChart Numbering System

• All charts are assigned a 1 to 5 digit number, All charts are assigned a 1 to 5 digit number, depending on the scale of the chartdepending on the scale of the chart

• No. of digitsNo. of digits ScaleScale– 11 no scale (supporting no scale (supporting

publications)publications)– 22 1:9,000,001 and smaller1:9,000,001 and smaller– 33 1:2,000,001 to 1:9,000,0011:2,000,001 to 1:9,000,001– 44 misc and special non-nav chartsmisc and special non-nav charts– 55 1:2,000,000 and larger1:2,000,000 and larger


• 1 Digit: supporting publications1 Digit: supporting publications

• 2 or 3 Digits: depict large ocean 2 or 3 Digits: depict large ocean basins and subdivisions. First digit basins and subdivisions. First digit is the ocean basin (there are nine is the ocean basin (there are nine worldwide).worldwide).

Ocean Basins of the WorldOcean Basins of the World


• 5 Digits: are of suitable scale to depict 5 Digits: are of suitable scale to depict coastal regions with the great detail coastal regions with the great detail necessary for piloting.necessary for piloting.– There are nine coastal regions in the worldThere are nine coastal regions in the world– Each is divided into several subregionsEach is divided into several subregions

• The first number is the regionThe first number is the region

• The second number is the subregionThe second number is the subregion

• The last three numbers represent the The last three numbers represent the geographic sequence of the chartgeographic sequence of the chart

Coastal Regions of the Coastal Regions of the WorldWorld


• Thus, the chart numbering systemThus, the chart numbering system– indicates the scale of the chart (by the indicates the scale of the chart (by the

number of digits in the chart number)number of digits in the chart number)– indicates the area of the world depicted indicates the area of the world depicted

(ocean basin, subdivision, coastal (ocean basin, subdivision, coastal region, and subregion)region, and subregion)

– enables the navigator to organize the enables the navigator to organize the charts into portfolioscharts into portfolios

Chart ScaleChart Scale

• An important point to remember:An important point to remember:

SMALL SCALE = LARGE AREASMALL SCALE = LARGE AREA

LARGE SCALE = SMALL AREALARGE SCALE = SMALL AREA

Chart and Publication Chart and Publication Correction SystemCorrection System

• Navigation is constantly changing!Navigation is constantly changing!• It is not practical to constantly reprint It is not practical to constantly reprint

navigational charts and publications.navigational charts and publications.• DMA and NOS disseminate corrections DMA and NOS disseminate corrections

using two publications:using two publications:– Notice to Mariners (DMA, worldwide Notice to Mariners (DMA, worldwide

coverage)coverage)– Local Notice to Mariners (USCG, changes Local Notice to Mariners (USCG, changes

pertaining to U.S. inland waters)pertaining to U.S. inland waters)


• Corrections must be made Corrections must be made by handby hand to to the affected chart or publication.the affected chart or publication.

• Fortunately, not all changes are made. Fortunately, not all changes are made. The corrections are kept on file, The corrections are kept on file, using a correction card for each chart.using a correction card for each chart.

• Changes are then entered on a chart Changes are then entered on a chart when a ship is scheduled to operate when a ship is scheduled to operate in the area the chart covers.in the area the chart covers.


• Semiannually, DMA publishes a five Semiannually, DMA publishes a five volume summary of all corrections volume summary of all corrections for the previous six months.for the previous six months.

Other Correction ResourcesOther Correction Resources

• Broadcast Notice to MarinersBroadcast Notice to Mariners

• Worldwide Navigation Warning System Worldwide Navigation Warning System (NAVAREAS)(NAVAREAS)

• HYDROLANTS and HYDROPACSHYDROLANTS and HYDROPACS

• DMA Daily MemorandaDMA Daily Memoranda

• Special Warnings (USN or USCG)Special Warnings (USN or USCG)

• Automated Notice to Mariners System Automated Notice to Mariners System (ANMS)(ANMS)

lesson 02: terrestrial coordinate system/ chart projections and numbering learning...

Documents

basic reference points

similar reference points

key points

longitude meridians

equator slide

largest circle

equatorparallels of

perfect sphere