A significant problem facing geographical researchers who wish to compare migration and commuting flows over time is that the boundaries of the geographical areas, between which flows are recorded, often change. This chapter describes an innovative method for re-estimating the migration and commuting data collected in the 1981 and 1991 Censuses for the geographical units used in the 2001 Census. The estimated interaction data are provided as origin-destination flow matrices for wards in England and Wales and pseudo-postcode sectors in Scotland. Altogether, there were about 10,000 zones in 1981, 1991 and 2001, providing huge but sparsely populated matrices of 10,000 by 10,000 cells. Because of the changing boundaries during inter-censal periods, virtually no work has attempted to compare local level migration and commuting flows in the two decades, 1981-91 and 1991-2001. The re-estimated spatially consistent interaction flows described here allow such comparisons to be made and we use migration change in England and commuting change in Liverpool to demonstrate the value of these new data.
Abstract flows over time: A first step towards solving dynamic packing problems