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

0

500000

1000000

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2500000

3000000

10 30 50 70 90 110

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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:j.c.h.Stillwell@leeds.ac.uk