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1、Geo-InformationSystemsDefinitionorgeo-informationsystems.ThereareaboutasmanydefinitionsofGISsystemsastheremaybeactualsystemsaround.Usuallytheconceptcomprises:1)adatabasewithavarietyofspatialdatathatare(1)georeferencedinacompatibleway;(2)withaspatialandthematicresolutionthatissmallenoughtoreflect:
2、(3)forthethemesthatareincorporated;(4)atthescaleoftheareaforwhichthesystemisdesigned,allsignificantspatialdifferencesthatarepertinenttotheapplicationsforwhichthesystemismeant2)suitablesoftwaretoaccessthedatabaseandtoperformlogical,statisticalandcartographicoperationswiththedata.Itisfurtherdesirab
3、lethatanygeo-informationsystemfunctionsinanorganizationalstructurethatenables:(1)tokeepthedatareliableanduptodateand(2)toexchangedatawithinterestedparties(3)whilemaintainingconfidentialityofthedatawhereandwhennecessary.Mainapplicationfieldsforgeoinformationsystemsare:Managementorspatialnetworks,i
4、ncludingmaintenance,likepowersupply,telephoneandroads.Managementoflandrelatedactivitieslikeland-ownership(cadastre),realestatetaxation,agriculturalandforestmanagement,geophysicalexploration,archeologicalsitesetc.Urbanandregionalspatialplanning,analysisofpopulationandlandusedistributions,siteselec
5、tion,routeplanning,catchmentareastudies,environmentalinteractions,etc.Spatialobjectsandattributedata.EssentiallyanyGIScontainstwotypesofdata:(1)spatialobjectsorentities,oftenstoredinvariouslayersormaps.(2)Attributedatathatdescribefeaturesrelatedtothespatialobjects.Sometimestherelationissimple:ana
6、reaonaland-usemapmayonlyhaveoneattribute:itsland-useclass.However,oftentherelationmaybemorecomplex:spatialobjectshavemanyattributese.g.forbhouse:(1)streetnumberofinhabitants,etc.Orforamainsewer:(1)crosssection;(2)material(3)latestmaintenance;(4)depthunderstreetlevel(5)districtofficeresponsiblefor
7、itsmaintenanceetc.InmostGIStheattributedataarehandledinaclassicaldatabasestructure,oftenatelationaldatabaselikeOracleorDbaseIII,whileaspecialgraphicaldatabasedealswiththespatialdata.Thespatialobjectisthanrelatedthrough
