Topo50 Map Reading Guide · If you are going to use the coordinates from the map, you will need to...

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Used by New ZealandEmergency Services

Map Reading Guide1:50 000How to use a Topographic map

THiS GUidE pRovidES iNfoRMaTioN oN:

• datums

• projections

• theNewZealandtopographicmapseriesTopo50(andhowtoreadthem),and

• howtonavigateusingamap.

FurtherdetailedinformationondatumsandprojectionsinNewZealandcanbefoundin‘Where in the World are We: a Technical Guide to datums and projections in New Zealand’,availableontheLandInformationNewZealandwebsite www.linz.govt.nz/surveypublications.

Topo50 Map Reading Guide

CoNTENTS

Who makes topographic maps? ........................................................................................................................2

What is a topographic map?...............................................................................................................................2

Creating a map ......................................................................................................................................................3

Geodetic datums ...................................................................................................................................3

Map projections ....................................................................................................................................4

The parts of a Topo50 map ..................................................................................................................................5

Cover and back panel ...........................................................................................................................6

Datum and projection information panel ..........................................................................................7

How to read a Topo50 map ..................................................................................................................................8

Map scale ...............................................................................................................................................8

Distance ................................................................................................................................................10

Directions .............................................................................................................................................10

Bearings ...............................................................................................................................................11

Map symbols (the legend) .................................................................................................................12

Contour lines ........................................................................................................................................13

Relief shading ......................................................................................................................................14

Map coordinates .................................................................................................................................15

Geographical coordinates - latitude and longitude ......................................................................15

Grid coordinates - eastings and northings .....................................................................................16

How to quote a grid reference for a particular point ....................................................................17

planning a trip .....................................................................................................................................................19

Using a GpS .........................................................................................................................................................19

Using GPS with a map ........................................................................................................................20

The magnetic compass......................................................................................................................................21

Compass errors ...................................................................................................................................21

Features of a compass .......................................................................................................................22

Using your compass to reach a destination ...................................................................................22

Conversion of bearings ......................................................................................................................24

Simple uses of a map .........................................................................................................................................24

Orienting a map ...................................................................................................................................24

Finding your present position............................................................................................................25

Setting a course ..................................................................................................................................26

Glossary................................................................................................................................................................28

uide WHo MaKES TopoGRapHiC MapS?

NewZealandTopo50mapsareproducedandpublishedbyLandInformationNewZealand(LINZ).

Topo50mapsareatascaleof1:50 000andshowgeographicfeaturesindetail.Theyareusefulforawiderangeofactivitiessuchaslocalnavigationbyvehicleoronfoot,localityareaplanningandstudyoftheenvironment.

LINZalsoproducessmallerscalemapsat1:250 000,1:500 000,1:1 million,and1:2 millionscales.Thesemapsareusefulforplanningtraveloverlargedistances,orforgivinganoverviewofNewZealand.

Mapsareusedbyawidevarietyofgroupsincludingthemilitary,emergencyservices,andrecreationaluserssuchastrampers.

WHaT iS a TopoGRapHiC Map?

Topographicmapsaredetailed,accurategraphicrepresentationsoffeaturesthatappearontheEarth’ssurface.Thesefeaturesinclude:

• Cultural: roads,buildings,urbandevelopment,railways,airports,namesof placesandgeographicfeatures

• Hydrography: lakes,rivers,streams,swamps,tidalflats

• Relief: mountains,valleys,slopes,depressions

• vegetation: woodedandclearedareas,vineyardsandorchards.

Thelevelofdetailshownonamapdependsonthescaleofthemap;smallscalemapsarelessdetailedthanlargerscalemaps.

CREaTiNG a Map

Portrayingfeaturesonthecurvedsurfaceoftheearthontoaflatmaprequirestheuseofageodeticdatumandmapprojection.

Geodetic datumsMappingandcoordinatesystemsarebasedonageodeticdatum,whichisamathematicalsurfacethatbestfitstheshapeoftheEarth.NewZealand’spreviousdatum-NewZealandGeodeticDatum1949(NZGD49)-wasdefinedin1949andbestfittedtheshapeoftheEarthintheNewZealandregiononly.

In2000,anewnationalgeocentricdatumwasadoptedinNewZealand-theNewZealandGeodeticDatum2000(NZGD2000).ThisdatumisbasedonamathematicalsurfacethatbestfitstheshapeoftheEarthasawhole.ItsoriginisattheEarth’scentreofmass,hencetheterm‘geocentric’.ThedatumalsoincorporatesadeformationmodelusedtomanagedeformationacrossNewZealandasaresultofplatetectonics.Formostuserstheseeffectscanbeignored.

TheprimaryreasonforthechangefromNZGD49toNZGD2000isthewidespreaduseofGlobalSatelliteNavigationSystems(GNSS)suchastheGlobalPositioningSystem(GPS).ThisisbasedonageocentricdatumknownastheWorldGeodeticSystem1984(WGS84).TheTopo50mapseriesusesNZGD2000.Formostpracticalpurposes,WGS84andNZGD2000coordinatesarethesame.

Onamap,datumcoordinatesareexpressedintermsoflatitudeandlongitude.Theseareoftenreferredtoasgeographicalcoordinates.

AsignificantimplicationofthechangefromNZGD49toNZGD2000isthatlatitudeandlongitudevaluesdifferfromtheirNZGD49predecessorsbyapproximately190mNand10mE.Whilefeaturesonthegroundwillnotmove,theircoordinateswillchangebyapproximately200minanortherlydirectionwhenmovingtotheNZGD2000datum.

HiNT: Remember, if you’re using a map that is in terms of NZGd49 your GpS may show your location as being approximately 200m different

uide Map projections

AmapprojectionenablesthecurvedmathematicalsurfaceapproximatingtheEarthtoberepresentedonaflatsheetofpaper(i.e.amap).Manyprojectionscanbedefinedintermsofaparticulargeodeticdatum.

Theprojectionprocessresultsinthemap’sspatialrepresentationbeingdistorted.Imaginestretchingandtearingabasketballtomakeitscurvedsurfacelieflatontheground.Themagnitudeofthedistortioncanbecalculated,allowingcorrectionstobemadewhennecessary.

Therearemanydifferenttypesofprojection,eachhavingitsownadvantagesanddisadvantages.Noprojectionisperfect.Theprojectionchosenforamapwillhaveminimal,oracceptable,distortionrelativetothemap’sscaleandpurpose.

Mapprojectionsgenerallyusearectangulargridcoordinatesystem.Thesegridcoordinatesaredescribedintermsofeastingandnorthing,thedistanceseastandnorthofanorigin.Theoriginisassignedasetofcoordinatesandthisisoftentermedthefalseorigin.Gridcoordinatesareusuallyexpressedinunitsofmetres.

TheTopo50mapseriesusestheNewZealandTransverseMercator2000(NZTM2000)projection.Theprevious1:50000NZMS260mapseriesusedadifferentprojectioncalledtheNewZealandMapGrid(NZMG).

THE paRTS of a Topo50 Map

ThetwomainpartsofaTopo50mapare:

• themapface,whichshowstheareamappedandincludesinformationtohelpyouvisualiseorrecognisetheareaandlocatefeaturesonthemap;and

• themapmargininformation,whichgivesdetailstohelpyouusethemap,aswellasexplanationsonwhen,whereandhowtheinformationwascompiled.

Topo50 Map of CHRiSTCHURCH (BX24)

uide Cover and back panel

OnaTopo50mapacoverpanelshowsthemapsheetnameandindicatestheareaofthemapandsurroundingmapsheets.

Thebackpanelshowsthegenerallocationofthemap,thepublicationdateofthemap,wherefurtherinformationcanbefound,andimportantlimitationswithinformationshownonthemap.

Mapsareproducedfrominformationavailableonacertaindate.Overtime,thatinformationmaychange.TheTopo50mapshaveapublisheddate.TherewillbemapsontheLINZwebsiteatwww.linz.govt.nzshowingthedateparticularareaswerelastmaintainedsouserscanseetheageofthedataonanyparticularmap.

fRoNT aNd BaCK CovER paNElS of Topo50 Map of CHRiSTCHURCH (BX24)

datum and projection information panelInformationonthedatumandprojectionusedareshownontheinformationpanelofaTopo50map.

dETailS pRovidEd oN a Topo50 Map

uide HoW To REad a Topo50 Map

Thefirststepinreadingatopographicmapistobecomefamiliarwiththespecificcharacteristicsofthemapormapsyou’reusing.

Openupyourmap,checkitcoverstheplacesofinterestandthenfindthefollowingcharacteristics:

HiNT: pay attention to how your map unfolds so you can fold it up again correctly

Map Scale• What is the map scale?Amaprepresentsagivenareaontheground.Amapscalereferstotherelationship(orratio)betweendistanceonamapandthecorrespondingdistanceontheground.Themapscaletellsyouaboutthecomparativesizeoffeaturesanddistancesdisplayedonthemap.

• Which direction is north?Thisisimportantbecausethenorthpointorientsthemaptotherealworld.

• What symbols are used on the map?Havealookatthelegend.Tounderstandthemapyouneedtounderstandthesymbolsused.Featuresthatappearonmapswithdifferentscalesmaybedepictedbydifferentsymbols.

What datum and projection is used?Ifyouaregoingtousethecoordinatesfromthemap,youwillneedtodeterminewhichcoordinatesystem(ordatum)andprojectionisusedonthemap.Alwaysincludeareferencetothedatumorprojectionwhenquotingcoordinates.Datumsandprojectionsareexplainedearlierinthisbooklet.Thisinformationwillbecontainedinthetextonthemapfooter(seeprevioussection‘Datumandprojectioninformationpanel’).

Ifyou’reusingaGlobalNavigationSatelliteSystem(GNSS)suchastheGlobalPositioningSystem(GPS),remembertosetyourGNSSreceivertothesamecoordinatesystemasyourmap,oracompatibleone.MapsonNewZealandGeodeticDatum2000(NZGD2000)datumarecompatiblewithWGS84usedinGNSS.

TheTopo50mapsareatascaleof1:50000.CommonscalesforNewZealandtopographicmapsare:

Scale Ground distance of 1cm on the map

Larger

Smaller

1:50000 500m

1:250000 2.5km

1:1million 10km

1:2million 20km

Toexplainscalesgraphically,lookata1:50000scaleTopo50map.Thefirstnumberofthescale(1)representsacoreunitofdistanceonthemap,whilethesecond(50000)representsthatsamedistanceontheground.

Inthiscase,onecentimetreonthemaprepresents50000centimetres,or500metres,ontheground.ThedistancebetweenTrigsA582andMQZGonthefollowingmapismeasuredat9cmatthemapscale,whichequatesto4.5kmontheground.

EXaMplE of SCaliNG diSTaNCE of a Topo50 Map (NoT To SCalE)

Thelargerthescaleofamap,thesmallertheareathatiscoveredandthemoredetailedthegraphicrepresentationoftheground.Forexample,smallscalemaps(suchas1:250000)aregoodforlongdistancevehiclenavigation,whilelargescalemaps(1:50000)areidealfortravelonfoot.

uide distance

Inadditiontothemapscale,mostmapsalsoshowascalebar:

SCalE BaR foR a Topo50 Map (NoT To SCalE)

Usingthescalebaronamapyoucandeterminethedistancebetweentwopointsonthemap.

HiNT: Use a piece of string, ruler or strip of paper to measure the distance between two points on the map. Then hold the right hand end of the measurement on a whole number of kilometres on the scale so the other end of the measurement is to the left of the 0 marker and note the whole number of kilometres (right hand point measurement). add to this the percentage of a kilometre read to the left of the zero marker

directionsMapsusuallyincludeanorthpointdiagraminthemapmargininformation.ThisshowsthedirectionofGridNorthandMagneticNorthatthecentreofthemap.

EXaMplE of a NoRTH poiNT diaGRaM oN a Topo50 Map

• True North(TN)isthedirectiontotheEarth’sgeographicNorthPole.

• Grid North(GN)isthedirectionoftheblueverticalgridlines(eastings)onaTopo50map.TheangulardifferencebetweenGNandTNisknownasgridconvergence.

• Magnetic North(MN)isthedirectionfromanypointonthesurfaceoftheEarthtowardstheEarth’sNorthMagneticPole.TheangulardifferencebetweenTNandMNisknownasMagneticDeclination.AsGNisusedinpreferencetoTNformapreadingpurposes,itismoreusefultoknowthedifferencebetweenGNandMN.ThisisknownastheGrid/Magneticangle.ThisvariesacrossNewZealandandbecausethepositionoftheNorthMagneticPolemovesslightlyfromyeartoyear,theGrid/MagneticangleandMagneticDeclinationwillvarybyasmallamounteachyear.Inusingamapforaccuratenavigation,magneticvariationcanbeimportant,particularlyifthemapisseveralyearsold.

BearingsDirectionscanalsobeexpressedasbearings.Abearingistheclockwisehorizontalanglemeasuredfromnorthtoachosendirection.Bearingsareusuallyshownindegreesandrangefrom0°(north)to360°(alsonorth).Southis180°,eastis90°,westis270°.Bearingsareoftenusedfornavigatingbetweenpoints.

illUSTRaTioN dEpiCTiNG BEaRiNGS of 40° aNd 320°

a CoMpaSS RoSE aNd BEaRiNG GUidE

uide Map symbols (the legend)

Mapsusesymbolstorepresentfeaturesontheground.Thesefeaturesincluderoads,tracks,rivers,lakes,vegetation,fences,buildings,powerlinesetc.Giventhesizeofamap,itisnotpossibletoshowallfeaturesontheground.Largescalemapsshowmoredetailandalargernumberoffeatures.Dependingonthescaleofthemaps,featuresmayhavetobeoffsetsotheycanbeclearlyshownonthemap,e.g.aroadwayandarailwaylinemayhavetobeseparatedhorizontallysotheydon’toverlayeachother.

Colourplaysanimportantpartinsymbolsandsomeinternationalconventionsapplytotheuseofcolour.Forexample,blueforwaterfeatures,blackforcultureandgreenforvegetation.

Symbolsaregroupedinthemesonthelegend.Whilemostsymbolsareeasilyrecognisedasthefeaturestheyrepresent,youcanalwaysrefertothemap’slegend.

paRT of a lEGENd fRoM a Topo50 Map

Contour linesTopo50mapsshow20mcontourlines.Theselines,whichjoinpointsofequalheight,representthereliefintheterraindepicted.Forexample,iftherearemanycontourlinesclosetogether,theterrainissteep.Contourlinesthatarefarapartindicatelandwithgentleslopes.Theaccuracyofacontourlineisusuallytakentobeabouthalfthecontourinterval,i.e.10monaTopo50map.

Thecoastlineonamaprepresentsthelineofmeanhighwaterlevel(MHW).However,contoursrepresenttheheightsabovemeansealevel(MSL).

HiNT: Contour values read uphill. as you read the contour numbers, you will be looking up hill

EXaMplE of CoNToUR SHapES (NoT To SCalE)

uide Relief shading

Inadditiontocontourlines,reliefshadinghelpsyouvisualisetheterrain.Hillsandvalleysareshadedasiftheywereilluminatedfromthenorth-west.

EXaMplE of REliEf SHadiNG (NoT To SCalE)

Map coordinatesMapcoordinatesareusuallyshowninoneoftwoways:

• geographical coordinates,givenaslatitudeandlongitudevaluesindegrees,minutesandseconds,e.g.NewZealandGeodeticDatum2000geographicalcoordinates;or

• grid coordinates,givenaseastingandnorthingvalues,inmetres,e.g.NewZealandTransverseMercator2000projectiongridcoordinates.

Topo50mapsshowageographicgraticule(latitudeandlongitude,indegrees,minutesandseconds)andacoordinategrid(eastingsandnorthings,inmetres),soyoucandeterminerelativeandabsolutepositionsofmappedfeatures.

EXaMplE of Map CooRdiNaTES USEd oN a Topo50 Map (NoT To SCalE)

Geographical coordinates - latitude and longitudeYoucanfindorexpressalocationusingthegeographiccoordinatesoflatitude(northorsouth–horizontallines)andlongitude(eastorwest–verticallines).

Latitudeistheangularexpressionofthedistancenorthorsouthfromtheequator(0°latitude).TheSouthPoleisat90°S;theNorthPoleat90°N.

LongitudeistheangularexpressionofthedistanceeastorwestfromtheimaginarylineknownasthePrimeMeridianat0°longitude.

Geographicalcoordinatesaremeasuredindegrees(°),minutes(‘)andseconds(“).Eachdegreeisdividedinto60minutes;eachminuteisdividedinto60seconds.Whenexpressingcoordinates,

uide latitudeisgivenfirst.Forexample,thegeographicalcoordinatesforTrigA5MHonthemap

followingwouldbestatedas:43°44’55”S172°37’00”E.

OntheTopo50mapsthelatitudeandlongitudecoordinatesareshownalongtheedgesofthemapfaceasblacklineswithshortblackmarkersthatindicatetheminutesoflatitudeandlongitude.

WaRNiNG: The lines of latitude and longitude which join the black tick marks on Topo50 maps are not parallel to the grid because of the effects of the Earth’s curvature and projection used

EXaMplE of laTiTUdE aNd loNGiTUdE liNES aloNG THE EdGE of a Topo50 Map (NoT To SCalE)

Grid coordinates - eastings and northingsGridlinescanalsobeusedtofindorexpressalocation.Gridlinesaretheequallyspacedverticalandhorizontalintersectinglinessuperimposedovertheentiremapface.Eachlineisnumberedattheedgeofthemapface.On1:50000Topo50maps,thedistancebetweenadjacentlinesis2cmwhichrepresents1000metres.

OfficialLINZmapsareprintedsogridnorthpointstothetopofthesheet.Onesetofgridlinesrunsnorth-south,whiletheotherrunswest-east.Thepositionofapointonthemapisdescribedasitsdistanceeastfromanorth-southlineanditsdistancenorthofaneast-westline.

Forthisreason,gridlinesarealsocalled:

• eastings–thesearetheverticallinesrunningfromtoptobottom(northtosouth).Theydividethemapfromwesttoeast.Theirvaluesincreasetowardstheeast;and

• northings–thesearethehorizontallinesrunningfromlefttoright(westtoeast).Theydividethemapfromnorthtosouth.Theirvaluesincreasetowardsthenorth.

Thesquaresformedbyintersectingeastingsandnorthingsarecalledgridsquares.OnTop50mapseachsquarerepresentsanareaof100hectaresoronesquarekilometre.

How to quote a grid reference for a particular pointAgridreferenceisusedtodescribeauniquepositiononthefaceofthemap.Thedegreeofaccuracyrequiredwilldeterminethemethodusedtogenerateagridreference.Allmethodsfollowasimilarapproach.ThetwotablesbelowdescribehowtogiveasimplifiedsixfiguregridreferenceandafullnorthingandeastinggridcoordinateforMtCavendishshownonTopo50mapBX24.

Thesimplifiedwayofexpressingthefullgridcoordinateistospecifythesheetnumberandasixfiguregridreference.Remembertoquotethesheetnumberasthesixfiguregridreferenceisnotuniquetoasinglesheet.

HoW To REad a SiX fiGURE GRid REfERENCE oN a Topo50 Map foR MT CavENdiSH

HiNT: if a grid reference starts with a zero, remember to include it

Afullgridcoordinatetothenearest100misgivenbyasevenfigureeastingandnorthingfortheexampleabove.

uide HoW To REad a fUll GRid REfERENCE oN a Topo50 Map foR MT CavENdiSH

To GivE aN EaSTiNG aNd NoRTHiNG GRid CooRdiNaTE oN THiS Map(Notethatthisexamplegivesthecoordinatetothenearest100metres)

SaMplE poiNT Mt Cavendish

East Coordinate

1.Recordthefirsttwodigitsofthefulleasting(E)giveninthebottomleftcornerofthemapmargin.Thesearethefirstandsecondnumbersoftheeastinggridcoordinate.

2.LocatethefirstVERTICALgridlinetotheLEFTofthesamplepoint.

3.Readthegridvalueslabellingthelineineitherthetoporbottommarginoracrossthemiddleofthemap.Thesearethethirdandfourthnumbersoftheeastinggridcoordinate.

WaRNiNGIfthesenumbersarelessthanthethirdandfourthnumbersinthebottomleftcornervaluesofthemap,add1tothefirsttwodigits.

4.Estimatetenthsofagridsquareeastwardfromthegridlinetothepoint.Thisisthefifthnumberofthefulleastinggridcoordinate.

5.Thefinaltwonumbersofthefulleastinggridcoordinateare00aswecanonlyestimatethereferencetothenearest100metres.

1577100

North Coordinate

1.Recordthefirsttwodigitsofthefullnorthing(N)giveninthebottomleftcornerofthemapmargin.Thesearethefirstandsecondnumbersofthenorthinggridcoordinate.

2.LocatethefirstHORIZONZTALgridlineBELOWthesamplepoint.

3.Readthegridvalueslabellingthelineineithertheleftorrightmarginofthemap.Thesearethethirdandfourthnumbersofthenorthinggridcoordinate.

WaRNiNGIfthesenumbersarelessthanthethirdandfourthnumbersinthebottomleftcornervaluesofthemap,add1tothefirsttwodigits.

4.Estimatetenthsofagridsquarenorthwardfromthegridlinetothepoint.Thisisthefifthnumberofthefullnorthinggridcoordinate.

5.Thefinaltwonumbersofthefullnorthinggridcoordinateare00aswecanonlyestimatethereferencetothenearest100metres.

5173700

SaMplE CooRdiNaTE 1577100 mE 5173700 mN

plaNNiNG a TRip

Planningasuccessfulroutethroughroughcountryusuallyrequiresatopographicmap,acompass,perhapsaGlobalNavigationSatelliteSystem(GNSS)receiversuchasaGlobalPositioningSystem(GPS)receiver,andobservationofvariouslandforms.Streamsandvegetationcanhelpwithnavigationbutmayhinderyourprogress.

Makesureyouhavetherightscalemapforthetripyouareplanning.Obviously,journeysonfootshouldbesupportedbyalargerscalemap,orsetofmaps.

Often,routefindingdoesnotrequiregreataccuracy,butitdoesrequireplanning.Beforesettingout,studythemap.Findyourstartandfinishpoints.Theterraindepictedonthemapwillhelpyouselectasuitableroute,andanticipateandmakebestuseofthefeaturesyouwillencounter.

Forexample,youmaydiscoveraleadingspurormainridgethatwillhelpyouavoidarivervalleywithcliffsorsteepterrain.Youwillalsobeabletomeasuretheroute’sdistanceandanyheightstoclimb,allowingyoutoestimatehowlongeachstageofthetripwilltake.

USiNG GpS

TheGPSisoneofanumberofGNSSandhasbeendevelopedbytheUSA’sDepartmentofDefense.Itiswidelyusedforciviliannavigationandpositioning,surveyingandscientificapplications,andalthoughanexcellenttool,itisbestusedwithamap.

GPSreceivershavemanyusefulfeaturesfornavigation,suchastheabilitytostorepositionsanddeterminespeedanddirectionoftravel(whicharebeyondthescopeofthisguide).Provideditisusedcorrectly,acomparativelyinexpensive,hand-heldGPSreceivercanprovidepositionswithaccuracybetterthan15mandoftenatthe5mlevel.

NoTE: a GpS is no substitute for a map and compass

EXaMplES of GpS RECEivERS

uide Using GpS with a map

AGPSreceivercalculatespositionbymeasuringdistancestofourormoreGPSsatellites.GPSisaccessible24hoursaday,anywhereintheworld,inallweather.

GPSisbasedontheWGS84datum(seeexplanationofdatumsonpage3).

ForpracticalpurposesNZGD2000canberegardedasthesameasWGS84.Itisimportanttocheckwhichdatumyourmapisbasedupon.

HiNT: Set your GpS datum to match your map datum

Thisdatuminformationwillbeshowninthemapmargin.ForthebestmatchbetweenyourmapcoordinatesandGPSreceiver,configuretheGPSreceivertodisplaycoordinates(geographicalorgrid)onthesamedatumasthemapbeingused.

MostGPSreceivershavetheabilitytodisplayeithergeographicorgridcoordinatesonanumberofnationalandregionaldatums.Itisimportanttoknowhowtosetthecorrectdatuminyourreceiver.PleaseconsultyourGPSreceiver’suserguidefordetails.Ifthedatumyouneedisnotofferedinyourreceiver,consultyourGPSdealerforassistance.

ItisrecommendedpracticetocheckyourGPSreceiveragainstwell-definedmapfeatureseverytimeyouuseit.Visitafeaturesuchasaroadintersection,determineitspositionbyGPSandcomparethiswithcoordinatescalculatedfromamap.Thelargerthescaleofthemapthebetter.Thecoordinatesofsurveycontrolmarksortrigpoints,maybeobtainedfromtheLINZgeodeticdatabaseatwww.linz.govt.nz/gdb

THE MaGNETiC CoMpaSS

Amagneticcompassisanimportantaidtoroute-findingandanyonewhoventuresintotheoutdoorsshouldcarryone.

Acompassworksontheprinciplethatthepivotingmagnetisedneedle(orthenorthpointoftheswingingdial)alwayspointstothenorthmagneticpole.

Asaresult,youcanuseacompasswithgraduations(degrees)markedonittomeasurethebearingofachosendirectionfrommagneticnorth.

HiNT: Metal objects such as cars, fence posts and wires, steel power poles and transmission lines, can affect the accuracy of a compass reading. Stand clear of such items when using a compass – at least 1m from metal fence posts and wires and up to 20m from a car

Compass errorsGeologicalfeaturessuchasironoredepositsanddoleriterockthathasbeenstruckbylightningcanaffectacompass.Itisevenpossiblefortheneedletobecomereverse-polarisedifitisstoredforalongtimenearastronglymagnetisedobject.

Itisthereforeadvisabletotreatmagneticbearingswithcautionandtochecktheaccuracyofyourcompass.Determinemagneticbearingsbetweenobjectsatleastonekilometreapart,usinginformationavailablefromamapandcomparethemwithyourcompassbearing.Thisshouldberepeatedindifferentdirections.

Checkforlocalanomaliesbyreadingbearingsbetweenobjectsabout100metresapartinoppositedirections–thebearingsshoulddifferby180degrees.

uide features of a compass

Therearemanytypesofcompasses.Thepivotedneedle,adjustabledialcompassisthemostusefultype.Seeexample–Silvacompassbelow.

Aswellasanorth-pointingNeedle,itwilloftenhaveatransparentbasewithaDirectionofTravelArrowandOrientingLinesmarkedontheRotatingDialhousing,soitcanbeusedasaprotractorformeasuringgridbearingsonamap.

fEaTURES of a TypiCal CoMpaSS

Using your compass to reach a destinationTofollowcompassbearingstoyourchosendestination,youwilleitherneedtodeterminemagneticbearingstovisiblefeaturesalongtheroute,orwillalreadyhavethesebearings.

To dETERMiNE MaGNETiC BEaRiNGS:

1Selectavisiblefeaturealongtherouteyouwanttotravel.Holdingthecompasslevel,pointtheDirectionofTravelArrowatthevisiblefeature.

2FindyourbearingtothevisiblefeaturebyturningtheCompassDialuntilthe“N”alignswiththeredendoftheNeedle.ReadyourbearingindegreesattheIndexLine.

3KeepingtheNeedlealignedwiththe“N”,proceedinthedirectionindicatedbythebearingattheIndexLine.Thebearingwillhelpyoukeepontrackwhenthefeatureisnotvisible.Repeatthisprocedureuntilyoureachyourdestination.

WHEN MaGNETiC BEaRiNGS aRE KNoWN:

1Ifyou’vebeengivenabearingindegreestotravel,turnthedialsothatthebearingissetattheIndexLine.Holdthecompasslevelinfrontofyou,withtheDirectionofTravelArrowpointingstraightahead.

2TurnyourbodyuntiltheredendoftheNeedleisalignedwiththe“N”onthedial.Youarenowfacingyourdirectionoftravel.

3Pickoutavisiblefeatureinlinewithyourbearingandwalktoit.Repeattheprocedureuntilyoureachyourdestination.

uide Conversion of bearings

Magneticbearingsmeasuredwithacompassmustbeconvertedtogridbearingsforplottingonamap.Similarly,gridbearingsmeasuredonamapmustbeconvertedtomagneticbearingsforcompassnavigationontheground.

Thegrid/magneticangleisthedifferencebetweengridnorthandmagneticnorthandisapositivevalueifmagneticnorthitiseastofgridnorthandanegativevalueifitiswestoftruenorth.

Toconvertfromamagneticbearingtoagridbearing,addthegrid/magneticangletothemagneticbearing.Toconvertagridbearingtoamagneticbearing,subtractthegrid/magneticangle(seepage10).

HiNT: G M S rule is: Grid to Magnetic Subtract (Good Morning Sunshine)

Eg,GridBearing62OGrid/Magneticangle-20OMagneticBearing=42O

SiMplE USES of a Map

orienting a mapItisagoodhabittoorientyourmapbeforereadingit.Todothis,holdyourmaphorizontallyandrotateituntilitsdirectionandfeaturescorrespondtowhatyouseebeforeyouontheground.

Ifyouareunabletoidentifythesurroundingfeatures,youcanusethecompasstoorientthemap.Todothis:

• Holdthemapflat.Placethecompassonthemapsothatthelongedgeofthebaseplate,oralineintheadjustabledial,sitsoverorisparalleltoanorth-southgridline.Ensurethatthe‘N’onthedialpointstonorthonthemap.

• Turnthemapwiththecompassonituntilthemagneticneedlepointstothemagneticvariation(whichisapproximately20°currently).

Oncethemapisoriented,youshouldbeabletoidentifyprominentfeaturesinthelandscape.

finding your present positionIfyouhaveaGPSreceiver,youcanuseittodetermineyourcoordinates,rememberingtosetittoadatumcorrespondingtothedatumonyourmap.Or,onceyoucanidentifysurroundingfeaturesonthegroundandonthemap,youcanusethefollowingproceduretofindyourcurrentposition.

HiNT: pack your map and compass in an easy-to-reach place. in wet weather, put the map, with the appropriate area displayed, in a clear plastic bag

1. Choosetwovisiblefeaturesandfindtheseonyourmap.NowpointtheDirectionofTravelArrowtowardsonefeatureandrotatetheCompassDialuntiltheredendoftheNeedlepointstothe“N”onthedial.

2. Addthegrid/magneticangletothebearingshownattheIndexLineandturnthedialtothenewbearing.

3. PlacethecompassonyourmapwiththesideedgeofthebaseplatetouchingthefeatureandpivotituntiltheOrientingArroworlinesalignwiththegridnorthlines.Drawalinefromthefeaturealongthesideofthebaseplateacrossthemap.

4. Repeatthisprocesswiththesecondfeature.Yourlocationiswherethetwolinesintersect.

uide Setting a course

Onceyouhaveorientedyourmapandidentifiedyourposition,youcansetacourse.Dothisbysightingorbylayingastraightline(usingtheedgeofthemapcardorapieceofstring)acrossthemap.Itisalsogoodpracticetoidentifyadistantvisiblefeatureontheline,suchasarockyoutcrop,andproceed.Thenidentifyanotherfeatureonthelineandsoonuntilyoureachyourdestination.

Whenfeaturesaresparse,youcoulduseaGPSreceiver.First,determinethecoordinatesofthedestinationpointfromthemapandenterthemintothereceiver,thenwalkintheapproximatedirectionofyourdestination,lettingthereceiverpointyouintherightdirectionasyougo.

HiNT: Check your map to determine if there are land features that may prevent you from following your GpS bearing

oR yoU CaN USE yoUR Map aNd CoMpaSS iN THiS Way:

1Beforeyoustartonyourway,placethecompassonthemapsothatthesideedgeofthebaseplateconnectsyourpresentpositiontoyourdestinationandtheDirectionofTravelArrowisalsopointingthatway.

2TurnthecompassdialuntiltheOrientingLinesareparallelwiththegridnorthlinesonthemapandtheOrientingArrowisalsopointingtogridnorth.

Topo50 Map Reading Guide3Thedial’sreadingattheIndexLineshowsthegridbearing.SubtracttheGrid/Magnetic anglefromthisbearingandturnthedialtoshowthenewmagneticbearingattheIndexLine.

4Putthemapaside.HoldthecompasssteadyandlevelinfrontofyouwiththeDirectionofTravelArrowpointingstraightahead.TurnyourbodyuntiltheredendoftheNeedleisdirectlyovertheOrientingArrow,pointingtothe“N”onthedial.TheDirectionofTravelArrownowpointstoyourdestination.Lookup,aligntheDirectionofTravelArrowwithafeatureandwalktoit.Repeatthisprocedureuntilyoureachyourdestination.

uide GloSSaRy

Bearing–geographicorientationofalinegivenasananglemeasurementindegreesclockwisefromtruenorth.

Cartography–theartandscienceofproducingmaps,chartsandotherrepresentationsofspatialrelationships.

Contour–alinedrawnonamapjoiningallthepointsontheEarththatarethesameheightabovemeansealevel.

Coordinates–angularorlinearvaluesthatdesignatethepositionofapointinagivendatumorprojectionsystem.

Coordinates, geographic–asystemofsphericalcoordinatescommonlyknownaslatitudeandlongitude.

Coordinates, grid–aplane-rectangularcoordinatesystemexpressedaseastingsandnorthings.

datum–amathematicalsurfaceonwhichamappingandcoordinatesystemisbased.

Elevation–theheightabovemeansealevel.

Geocentric datum–adatumwhichhasitsoriginattheEarth’scentreofmass.Theadvantageofthegeocentricdatumisitsdirectcompatibilitywithsatellite-basednavigationsystems.

Geographical coordinates–apositiongivenintermsoflatitudeandlongitude.

GpS–GlobalPositioningSystem–isasatellitebasednavigationsystemdevelopedbytheUnitedStatesDepartmentofDefenseandwidelyusedforciviliannavigationandpositioning.

GNSS–GlobalNavigationSatelliteSystem

Graticule–anetworkoflinesonamaporchartrepresentingtheparallelsoflatitudeandmeridiansoflongitudeoftheEarth.

Grid–twosetsofparallellinesintersectingatrightanglestoformsquares.

Grid convergence–theangulardifferencebetweenGridNorthandTrueNorth.

Grid coordinates–theequallyspacedverticalandhorizontalintersectinglinessuperimposedoverthefaceofamap.Onesetofgridlinesrunsnorth-south,whiletheotherrunswest-east.Thepositionofapointonthemapisdescribedasitsdistanceeastfromanorth-southlineanditsdistancenorthofaneast-westline.

Grid/magnetic (G-M) angle–thedifferencebetweengridnorthandmagneticnorthandisapositivevalueifmagneticnorthitiseastofgridnorthandanegativevalueifitiswestoftruenorth.

latitude–thelatitudeofafeatureisitsangulardistanceonameridian,measurednorthwardsorsouthwardsfromtheEquator.

longitude–anangulardistancemeasuredeastorwestalongtheequatorfromareferencemeridian(Greenwich).

Magnetic north–thedirectionasindicatedbyacompasstotheearthmagneticpole.

Map–arepresentationoftheEarth’ssurface.Acadastralmapisoneshowingthelandsubdividedintounitsofownership;atopographicmapisoneshowingthephysicalandsuperficialfeaturesastheyappearontheground;athematicmapdisplaysaparticulartheme,suchasvegetationorpopulationdensity.

Map projection–anysystematicwayofrepresentingthemeridiansandparallelsoftheEarthuponaplanesurface.

Mercator projection–theconformalcylindricalprojectiontangentialtotheEquator,possessingtheadditionalvaluablepropertythatallrhumblinesarerepresentedbystraightlines.Usedextensivelyforhydrographicandaeronauticalcharts.

Meridian–animaginarylinefromtheNorthPoletotheSouthPoleconnectingpointsofequallongitude.

NZGd49–NewZealandGeodeticDatum1949-alocaldatumthatwasabestfittotheshapeoftheEarthintheNewZealandregion.IthasnowbeensupersededbyNZGD2000.

NZGd2000–NewZealandGeodeticDatum2000–ageocentricdatumbasedonamathematicalsurfacethatbestfitstheshapeoftheEarthasawhole,withitsoriginattheEarth’scentreofmass.

NZMG–NewZealandMapGrid–aconformalmappingprojectionadoptedforNewZealandin1973withminimalscaleerror.BasedonNZGD49.

NZTM2000–NewZealandTransverseMercatorprojection2000-aTransverseMercatorprojectionbasedonNZGD2000.Theunitofmeasureisthemetre.

Relief–thedeviationofanareaoftheEarth’ssurfacefromaplane.ItreferstothephysicalshapeofthesurfaceoftheEarth.

Rhumb line–acurveonthesurfaceofaspherethatcutsallmeridiansatthesameangle;thepaththatmaintainsaconstanttruebearing.

Topography–descriptionorrepresentationonamapofthephysicalandculturalsurfacefeatures.

uide Transverse Mercator (TM) projection–aconformalcylindricalmapprojection,originally

devisedbyGauss,alsoknownastheGauss-Krugerprojection.Asitsnameimplies,itsconstructionisonthesameprincipleastheMercatorprojection,theonlydifferencebeingthatthegreatcircleoftangencyisnowanynominatedmeridian.Meridiansandparallelsarecurvedlines,exceptforthecentralmeridianforaspecifiedzone(meridianoftangency),whichremainsastraightline.Theamountofscaledistortionmaybecomeunacceptableatdistancesgreaterthanabout1.5degreesinlongitudefromthecentralmeridian.

WGS84–WorldGeodeticSystem1984–ageocentricgeodeticdatumdevelopedbytheUnitedStatesDepartmentofDefenseforusewithGPS.Formostpracticalpurposes,NZGD2000isequivalenttoWGS84.

uide ThisdocumenthasbeenadaptedfromMapReadingGuide,HowtouseTopographicMaps

byGeoscienceAustralia,GPOBox378,Canberra,ACT2609,Australia.ThanksaregiventoGeoscienceAustraliaforpermissiontousethisinformation.

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