Unit-23-GIS-Basic

Unit23GISBasicDefinitionsofGIS“GIS”isanacronymmeaningofGeographicInformationSystem,InordertoprovideagoodunderstandingofGIS,thefollowingtwodefinitionsgivenbyRhind(1989)andtheUnitedStatesGeologicalSurvey(USGS,1997)respectivelyarepresentedfirst.1.```asystemofhardware,software,andproceduresdesignedtosupportthecapture,manipulation,analysis,modeling,anddisplayofspatiallyreferenceddataforsolvingcomplexplanningandmanagementproblems.2.```acomputersystemcapableofassembling,storing,manipulating,anddisplayinggeographicallyreferencedinformation,i.e.,dataidentifiedaccordingtotheirlocation.GISbooksgenerallyadopttheideasexpressedbythesetwodefinitions.ThesetwocharacteristicsdistinguishGISfromothertypesofinformationsystems:Theword“Geographic”inGISexplains“spatially”wherethingsaresuchasthelocationofnations,states,counties,cities,schools,roads,rivers,lakes,andthelistcangoonandon.Spatiallymeanswhereontheearth’ssurfaceanobjectorfeatureislocated.Thiscanbeassimpleasthelatitudeandlongitudeofafeature.Thegeographicfeatureorobjectcanbeanythingofinterest.“Information”inGISisthe“data”or“attribute”informationaboutspecificfeaturesthatweareinterestedin.Thenameofthefeature,whatthefeatureis,thelocationofthefeature,andanyotherinformationthatisimportant.Anexamplecouldbethenameofacity,whereitislocated,howbigitisinsquarefeet(area),itspopulation,itspopulationinthepast.Andanyotherinformationisimportant.“System”inGISisthecomputersoftwarethatiswrittentohelppeopleanalyzethedata,lookatthedataandcombineitinvariouswaystoshowrelationshipsortocreategeographicmodels,AGIScanbemadeupofavarietyofsoftwareandhardwaretools,aslongastheyareintegratedtoprovideafunctionalgeographicdataprocessingtool.Asmentionedabove,GISiscomputersystemthatlinksgeographicinformation(wherethingsare)withdescriptiveinformationwhatthingsare.Unlikeaflatpapermap,wherewhatyouseeiswhatyouget,aGIScanpresentmanylayersofdifferentinformation.Touseapapermap,allyoudoisunfoldit.Spreadoutbeforeyouisarepresentationofcitiesandroads.Mountainsandrivers,railroads,andpoliticalboundaries.Thecitiesarerepresentedbylittledotsorcircles,theroadsbyblacklines,themountainpeaksbytinytriangles,andthelakesbysmallblueareasimilartothereallakes.Adigitalmapisnotmuchmoredifficulttousethanapapermap.Asonthepapermap,therearedotsorpointsthatrepresentfeaturesonthemapsuchascities,linesthatrepresentfeaturessuchasroadsandsmallareasthatrepresentfeaturessuchaslakes.Allthisinformation~~wherethepointislocated,howlongtheroadis,andevenhowmanysquaremilesalakeoccupies~~isstoredaslayersindigitalformatasapatternofonesandzerosinacomputer.Thinkofthisgeographicdataaslayersofinformationunderneaththecomputerscreen.Eachlayerrepresentaparticularthemeorfeatureofthemap.Onethemecouldbemadeupofalltheroadsinanarea.Anotherthemecouldrepresentallthelakesinthesamearea.Yetanothercouldrepresentallthecities.Thesethemescanbelaidontopofoneanother,creatingastackofinformationaboutthesamegeographicarea.Eachlayercanbeturnedoffandon,asifyouwerepeelingalayeroffthestackorplacingitbackon.Youcontroltheamountofinformationaboutanareathatyouwanttosee,atanytime,onanyspecificmap.ThetechnologycomponentsofaGIScanbeexplainedintermsofhardware,softwareandhumanresources.GIShardwareincludes:computers,computerconfiguration/networks,inputdevices,printers,andstoragesystems.ComputersforGISusagecanbePCsorsupercomputers.Thesecomputerscanbestand-aloneunitsorcanbehookedintoanetworkenvironment.Inputdevicesincludedigitizersandscanners.Printersandplottersareusedtoproduceahardcopymap.GISstoragesystemsinclude:opticaldisks,magneticdiskssuchasaharddrive,floppydisksormagnetictapes.GISsoftwareincludesbothGISprogramandspecialapplicationpackages,suchasdigitalterrainmodelingandnetworkanalysis.ThemaindifferencebetweenGISsoftwareprogramsanddesktopmappingprogramsistheabilityofGISprogramstoperformspatialanalysis.ARC/INFObyEnvironmentalSystemsReacherInstitute(ESRII)Inc.IsoneoftypicalexamplesofGISsoftwarepackages.Desktopmappingprogramsoffermanyofthesamefeatures,asaGIS,buttheirabilitytosupportspatialanalysesarelimited.Theyaredevelopedtosatisfyindividualuserneedsformappingpresentations.MapInfodevelopedbyMapInfoCorpisanexampleofpopulardesktopmappingprogram.HumanresourcesusedtooperateaGIStypicallyinclude:operationalstaff,technicalprofessionalstaff,andmanagementpersonnel.Operationalstaffarepeoplesuchas(1)cartographers,whomonitorthedesignofmapdisplay,thestandardsformapsymbolsandstandardmapseries,(2)datacapturers,whoconvertsmapintodigitalformand(3)potentialusersofaGIS,Technicalprofessionalstaffinclude(1)informationanalystswhosolveparticularuserproblemsandsatisfytheirinformationneeds,(2)systemadministrators,whoareresponsibleforkeepingthesystem(hardware/software)operational,(3)programmers,whotranslatetheapplicationspecificationspreparedbytheanalystintoprogramand(4)thedatabaseadministrator,whoassisttheanalysts,programmersanduserstoorganizegeographicfeaturesintolayers,identifysourceofdata,developcodingstructuresfornon-graphicsdata,anddocumentinformationaboutthecontentsofthedatabase.Managementpersonalinclude(1)themana