Industrial heterogeneity and spatial hierarchy in multiregional freight-generation models

Covariance analysis is used to explore two questions encountered in modelling freight generation for a multizonal system. At the level of the British standard region, where employment data by industry are readily available, experiments are conducted on a variety of aggregations of freight-flow data to see whether explanatory-variable data collection and manipulation can be minimized. This would be the case if common relationships between freight generated and employment data hold for broad groupings such as 'heavy' industry, chemicals, and engineering. At the zonal level an examination is made of the spatial distribution of residuals from the regression of total road freight generated on resident population. It is shown that for different zone types different relationships hold, and it is demonstrated that the centre - periphery explanation of the spatial distribution of residuals can be seen to be valid if 'centre' and 'periphery' are defined in a functional sense.