ComparingDistanceandItsFrictionalEffectonInternalMigrationinCountriesAround
theWorld
PresentationintheAlanWilsonPlenarySession- SpatialInteractionModelling- attheEuropeanColloquiumonTheoreticalandQuantitativeGeographyattheParkInn,
York,7September2017
John StillwellSchool of GeographyUniversity of Leeds
InternalMigration
MeasuresforCross-NationalComparisonofInternalMigration
Measures of migration intensity1 Crude Migration Intensity2 Standardized Migration Intensity3 Gross Migraproduction Rate4 Migration Expectancy5 Peak Migration Intensity6 Age at Peak IntensityMeasures of migration distance7 Mean Distance Moved8 Distance Decay Parameter9 Courgeau’s ‘K’Measures of migration connectivity10 Index of Migration Connectivity11 Index of Migration Inequality12 Migration Weighted Gini13 Coefficient of VariationMeasures of migration impact14 Migration Effectiveness Index15 Aggregate Net Migration Rate
Source: Bell, M., Blake, M., Boyle, P., Duke-Williams, O., Rees, P., Stillwell, J. and Hugo, G. (2002) Cross-national comparison of internal migration: issues and measures, Journal of the Royal Statistical Society A, 165(3): 435-464
Researchquestions
• Howfardomigrantsmoveindifferentcountriesaroundtheworld?
• Whatisthefrictionaleffectofdistanceindifferentcountries?
• Canweproduceleaguetablesoftheseindicators?
Impedimentstocross-nationalcomparison
• Lackofdataandaccesstodata• Differencesinconceptofmigration,e.g.migrantsversusmoves
• Disparitiesinthewayinternalmigrationdataarecaptured,processedandpublished
• Differencesintemporalandspatialframeworksusedformeasurement
Foradetaileddiscussion,seeBell,M.,Charles-Edwards,E.,Kupiszewska,D.,Kupiszewski,M.,Stillwell,J.,&Zhu,Y.(2014).InternalMigrationDataAroundtheWorld:AssessingContemporaryPractice.Population,SpaceandPlace, 21(1),1-17
ModifiableArealUnitProblem(MAUP)
• TheMAUPhastwocomponents(Openshaw,1984):
• Scaleeffect: Howdoesamigrationindicatorvaryaccordingtothenumberofregions(letscallthemAggregatedSpatialRegions(ASRs)?
• Zonationeffect: HowdoesamigrationindicatorvaryaccordingtotheconfigurationASRsatanyspatialscale(samenumberofASRs)?
TheIMAGEProject• Aninternationalcollaborativeprogramcomparinginternalmigrationbetweencountries
• FundedbyAustralianResearchCouncil
• Bell,Stillwell,Kupiszewski,Zhu,withCharles-Edwards,Daras,Kupiszewska,Ueffing,Rees,Bernard
• Collaboratorsfrom20countries
IMAGEInventory• Whocollectswhat?• 193UNmemberstates
IMAGERepository• Datasetsfor135nations
IMAGEStudio• Computesmigrationmetrics• Addressesmethodological
issues– theMAUP
IMAGEOutputs• Thematicpapers• Methodologicalpapers• Regionalpapers
StructureoftheIMAGEStudio
DataPreparationSystem:Needtoensurecontiguitiescomplete
AggregationSubsystem:IRAwavealgorithm
Example:BSUaggregationfortheUK
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Meantotalinter-ASR
migrants
Scale(NumberofASRs)
Start:n=420BSUsM=2.5millionCMI=4.2%
End:n=10ASRsM=1.1millionCMI=1.9%
IndicatorsSubsystem:GlobalandlocalindicatorsGlobalinformation
or Indicator1 Totalpopulation2 Area3 Populationdensity4 Totalmigrants5 Meanmigrationflow6 Medianmigrationflow7 Maxmigrationflow8 Minmigrationflow9 Crudemigrationintensity10 Aggregatenetmigration11 Aggregatenetmigrationrate12 Migrationeffectivenessindex13 Meanmigrationdistance(between)14 Meanmigrationdistance(within)15 Meanmigrationdistance(All)16 Medianmigrationdistance(between)17 Medianmigrationdistance(within)18 Medianmigrationdistance(All)19 Coefficientofvariation20 Indexofconnectivity21 Indexofinequality22 Theil index
LocalInformationor Indicator
1 Population2 Populationdensity3 Area4 Intraregionalflow5 Intraregionalrate6 Meanmigrationinflow7 Medianmigrationinflow8 Maxmigrationinflow9 Meanmigrationoutflow10 Medianmigrationoutflow11 Maxmigrationoutflow12 Netmigrationbalance13 Netmigrationrate14 Turnover15 Turnoverrate16 Churn17 Churnrate18 Migrationeffectivenessindex19 Coefficientofvariation20 Indexofmigrationinequality21 Indexofconnectivity22 Inflows23 Inflowrates24 Inflowmeanmigrationdistance25 Inflowmedianmigrationdistance26 Outflows27 Outflowrates28 Outflowmeanmigrationdistance29 Outflowmedianmigrationdistance
• IMAGEStudioallowschoiceofwhateverscalestepswewantplusthenumberofdifferentconfigurationsoftheBSUsateachscale
• Itthencomputestheselectedmigrationindicatorsateachscaleforeachconfigurationandgivessummarystatistics(e.g.mean,max.,min.,range)
ModellingSubsystem:SpatialinteractionmodelWeuseaSIMtogeneratetwomigrationindicators:
(i) Meanmigrationdistance(ii) Frictionaleffectofdistance(distancedecayparameter)
Thedoublyconstrainedmodelis:
M'ij =AiOiBj Dj dij-βwhere:M'ij isthepredictedflowofmigrantsfromareai toareajOi isthetotaloutmigrationfromareaiDj isthetotalin-migrationtoareajAiandBj arebalancingfactorstoensuretheconstraints
Oi =∑j M'ij and Dj =∑i M'ijDij isthedistancebetweenareai andareajβ isthedistancedecayparameter
BasicDataRequired
Foranycountryofinterest:I. anorigin-destinationmatrixofflows
betweenasetofBSUsII. digitalboundariesofthecorrespondingBSUsIII. populationsatrisk(PAR)oftherespective
BSUs
Datasetsused:Twosamples• Migrationmatricesareavailablefor105of193UNcountriesBUTwewantcountriesforwhichthereisasufficientlyfinelevelofspatialdetailtoenablescaleeffectstobemeasured- soweuseonlycountrieswith100ormoreBasicSpatialUnits
• Sample1:19countrieswith5yeardataSample2:13countrieswith1yeardata
• Nodataonintra-zonalmoves• RunStudiousingwaveaggregationroutineinstepsof10with200configurationsateachscale
• PresentmeanMMDandbetaforeachscale
Meaninter-zonaldistancesbyscaleFive-yearmigrationcountries One-yearmigrationcountries
• Graphsrevealthescaleeffectsforeachcountry,BUTthenumberofASRsisapoorbasisforcomparisonasASRsdifferbetweencountriesintermsofareaand/orpopulation
• Tomakemorerobustcomparisons,weusemeanareasizeateachspatialscaletoreplacethenumberofASRsonthehorizontalaxis
• WhencurvesarefittedtotheMMD-arearelationshipforeachcountryusingR,thebest-fitisrepresentedbyafunctionwhichcanbewrittenas:
MMD=a(A/n)b
whereA/n isthemeanASRareasizeatscalen anda andb areparametersthatdefinethefunction
ModelledrelationshipbetweenMMDandareasize
Five-yearmigrationcountries One-yearmigrationcountries
Meanmigrationdistancesforareasof100and500sq kilometres
Five-yearmigrationcountries One-yearmigrationcountries
DistancedecayparametersFive-yearmigrationcountries One-yearmigrationcountries
LeaguetablesatalternativepopulationsOne-yearmigrationcountriesFive-yearmigrationcountries
Conclusions• Cross-nationalcomparisonsofinternalmigration:
§ proveverychallenging§ requirespatialharmonisation
• IMAGEStudioisanattemptathandlingtheMAUPchallengewhentryingtomakecross-nationalcomparisons
• Spatialinteractionmodellingatdifferentlevelsofaggregationenablesustoobservescale(andzonation)effectsondistancemovedanddecayparameter
• Whereasthemeanmigrationdistancevarieswithscale,thedistancedecayparameterisscaleindependentandleaguetableshavebeengeneratedforbothindicators
• OngoingworkisinvestigatingMAUPeffectsoninter-districtflowsintheUKindifferentage,sex,ethnicandsocio-economicgroups
Thanksforyourattention
FurtherdetailsofIMAGEProjectavailableat:www.imageproject.com.au
IMAGEStudioandmanualavailableon
IMAGEStudiosetupfilehttps://github.com/IMAGE-Project/IMAGE_Studio_bin/releases
IMAGEStudiodatahttps://github.com/IMAGE-Project/IMAGE_Data
Contactdetails:[email protected]