Abstract
In this paper, we investigate the effects of scale and zone configuration on migration indicators and spatial interaction model parameters using a software system known as the IMAGE Studio. Internal migration flows in the United Kingdom and the local authority districts between which they move are aggregated into sets of increasingly fewer and larger polygons using alternative zone design algorithms. Indicators of migration intensity, impact and distance are revealed to vary significantly by scale but less so by zonation, whereas migration effectiveness and distance show greater scale independence but more sensitivity to zone configuration. Equal area and population optimised regions improve the quality of measures to a certain degree depending upon the imposition of shape constraints.
Highlights
Spatial analysts are familiar with the axiom that statistical indicators and model parameters that quantify different features of a particular human geographic phenomenonBrisbane, Qld 4072, Australia may vary with the spatial scale for which data are available and with the configuration of the zones for which data are reported at each scale
In order to investigate the speed at which the alternative processes in the IMAGE Studio produce solutions, we have experimented by selecting the local authority districts (LADs) administrative units and the United Kingdom (UK) 2011 Census internal migration flow data to aggregate the 404 Basic Spatial Units (BSUs) in steps of 1, 10, 20 and 50 with 10, 100, 500, 1000 aggregation iterations generated from random seeds at each step
As we have shown in the case of the UK, the intensity at which people move between regions depends upon the size and shape of the regions concerned and it is only when all internal migrations are included in an aggregate Crude Migration Intensity (CMI) that direct comparisons between countries can be made and national league tables constructed as reported in Bell et al (2015b)
Summary
Qld 4072, Australia may vary with the spatial scale for which data are available and with the configuration (or shape) of the zones for which data are reported at each scale This variation is attributable to the so-called ‘scale’ and ‘zonation’ effects of the Modifiable Areal Unit Problem (MAUP) that Openshaw (1984) documented carefully in his famous CATMOG publication and which has been addressed by a number of geographers since most recently by Lloyd (2014) and Manley (2014). Migration flows in the 12 month period before the 2011 Census in the United Kingdom (UK), for example, are available in the form of symmetric origin-destination matrices at certain spatial scales (Duke-Williams et al 2018) and the volume and intensity of migration between zones will be scale dependent. For example, the volume of migrants over 1 year of age between 404 local authority districts in the UK in the 12 months before the 2011 Census was around 2.8 million people and the crude migration intensity was 44.3 per thousand population, whereas only around 1.2 million individuals or 18.7 per thousand of the population moved between the 12 UK regions (2011 Census Special Migration Statistics extracted from UK Data Service using WICID)
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