ThediscussionsandexamplesinthissectionarebasedontheSectionalAeronauticalChart(Sectional).Sec-tionalsincludethemostcurrentdataandareatascale(1:500,000)mostbenecialtopilotsyingunderVisualFlightRules.Apilotshouldhavelittledifcultyinreadingthesechartswhichare,inmanyrespects,similartoautomobileroadmaps.Eachchartisnamedforamajorcitywithinitsareaofcoverage.
Thechartlegendlistsvariousaeronauticalsymbolsaswellasinformationconcerningterrainandcontour
elevations.Youmayidentifyaeronautical,topographical,andobstructionsymbols(suchasradioandtelevisiontow-ers)byreferringtothelegend.Manylandmarkswhichcanbeeasilyrecognizedfromtheair,suchasstadiums,pumpingstations,reneries,etc.,areidentiedbybriefdescriptionsadjacenttosmallblacksquaresmarkingtheirexactlocations
.Water,oilandgastanksareshownbysmallblackcirclesandlabeledaccordingly,ifknown.Thescaleofanitemmaybeincreasedtomakeiteasiertoreadonthechart.
NACOchartsarepreparedinaccordancewithspecicationsoftheInteragencyAirCartographicCommittee
(IACC)andareapprovedbyrepresentativesoftheFederalAviationAdministration(FAA)andtheDepartmentofDefense(DoD).
TERRAINANDOBSTRUCTIONS
TheelevationandcongurationoftheEarth's
surfacearecertainlyofprimeimportancetopilots.Car-tographersdevoteagreatdealofattentiontoshowingreliefandobstructiondatainaclearandconcisemanner.Fivedifferenttechniquesareused:contourlines,shaded
relief,colortints,obstructionsymbols,andMaximumElevationFigures.(MEF)
1.Contourlinesarelinescon-
nectingpointsontheEarthofequalelevation.OnSectionals,basiccon-toursarespacedat500'intervals.Intermediatecontoursmayalsobeshownat250'inter-valsinmoderatelylevelorgentlyrollingareas.Occasion-ally,auxiliarycontoursat50,100,125,or150'intervalsmaybeusedtoportraysmallerrelieffeaturesinareasof
relativelylowrelief.Thepatternoftheselinesandtheir
spacinggivesthepilotavisualconceptoftheterrain.Widelyspacedcontoursrepresentgentleslopes,whilecloselyspacedcontoursrepresentsteepslopes.
2.Shadedreliefisadepic-tionofhowtheterrainmightappearfromtheair.Thecartogra-phershadestheareasthatwouldappearinshadowifilluminatedby
alightfromthenorthwest.Studies
haveindicatedthatourvisualper-ceptionhasbeenconditionedtothisview.
3.Colortintsareusedto
depictbandsofelevation.Thesecol-orsrangefromlightgreenforthelowestelevationstobrownforthehigherelevations.
4.Obstructionsymbolsare
usedtodepictman-madeverticalfeaturesthatmayaffecttheNationalAirspaceSystem.NACOmaintainsa
leofover109,000obstaclesintheUnitedStates,Can-ada,theCaribbeanandMexico.Eachobstacleisevalu-
atedbycartographersbeforeitisaddedtothevisualcharts.Whenthepositionorelevationofanobstacleisunveried,itismarkedUC(underconstructionorreportedbutnotveried).ThedataintheDigitalObstacleFile(DOF)iscol-lectedanddisseminatedaspartofNACO’sresponsibilityfordepictingtheNationalAirspaceSystem.
Sourcedataonterrainandobstructionsissome-timesnotcompleteoraccurateenoughforuseinaero-nauticalpublications;forexample,areportedobstruction
maybesubmittedwithinsufcientdetailfordetermining
theobstruction'spositionandelevation.SuchcasesareidentiedbyNACOandinvestigatedbytheFAAFlight
Editprogram.TheFAAFlightEditcrewconductsdataverica-tionmissions,visuallyverifyingculturalandtopographicfeaturesandreviewingallobstacledata.Thisreviewincludescheckingforobstructionsthatmayhavebeenconstructed,altered,ordismantledwithoutpropernoti-cation.Unveriedobstaclesaresubsequentlyphoto-