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1、测绘专业英语1UNIT-24examplesoflinearfeatures.Theresolutionorscaleofgivendatasetonceagainplacesafundamentallimitationtoconceivethemashavinganywidth.Linearfeatures,unlikepointfeatures,allowustomeasuretheirspatialextent/length.Areafeatureshavetwodimensionsbothlengthandwidthdimensi
2、ons.Areaiscomposedofseriesoflinesthatbeginandendatthesamelocation.Wecandescribetheirshapesandorientations,andtheamountofterritoryoccupiedaswell.Indatabase,thetermpolygonisoftenusedinsteadofarea.Again,physicalsizeinrelationtothescaledetermineswhetheranobjectisrepresentedby
3、anareaorbyapoint.Itisoftenthatareaisdividedintoregularsquaresorrectanglessothatallobjectsaredescribedintermsofareas.Thisentiredatastructureiscalledagrid.Eachsquareorrectangularisknownasacellandrepresentsauniformvalue.Addingthedimensionofheighttoareafeaturesallowsustoobser
4、veandrecordtheexistenceofsurfaces.Surfaceshavethreedimensions—length,width,andheight.Forinstance,hills,valleys,andridgescanbedescribedbycitingtheirlocations,amountofareatheyoccupy,howtheyareoriented,andbynotingtheirheights.Attribute/TabularData—AddingInformationtoMapsAttr
5、ibutedataistheinformationaboutanobjectorfeature.Anexamplecouldbeourschool,itsname,location,whatdistrict,howmanychildrenattendeachyear,etc..Attributedataisusuallystoredinadatabase,tabular,orspreadsheettypeformat.Tabulardataisinformationdescribingamapfeature.Forexample,amap
6、ofcustomerlocationsmaybelinkedtodemographicinformationaboutthosecustomers.TabulardataforuseinaGIScanbepurchasedalreadypackagedwithspatialdataoritcanbefoundinyourownorganization.Ifyouhavelists,spreadsheets,ordatabasesaboutinformationlikecustomerlists,whereofficesarelocated
7、,orothers,youcanusethisinformationinaGIS.IfyouhavethecorrectspatialdatatheGIScanlinkyourtabulardatawiththespatialdata.Forexample,youcancreatepointsonamapofofficelocations.Oryoucanlinksalesinformationwithpostalcodeareas,allowingyoutomapsalesvolumebypostalcode.Tabulardatayo
8、ualreadyowncancombinedwithtabulardataforpurchasetohelpanalyzethedatabetter.Perhapsyou’dliketotak
