Delivering Census Interaction Data to the User: Data Provision and Software Development

The Census Interaction Data Service (CIDS) is a Data Support Unit providing access for researchers in the UK to the interaction data sets that are produced by the Census Offices. These migration and commuting data sets are large and complex, differing from the area statistics by virtue of the fact that they involve two geographies – one of origin and the other of destination. WICID, the web-based software system developed to provide the user interface to the Special Migration Statistics (SMS) and the Special Workplace Statistics (SWS) from the 1991 Census, has now been upgraded to allow registered users of census data to extract subsets of the 2001 interaction data sets. These include 2001 SMS and SWS as well as a new set of Special Travel Statistics (STS) for flows in Scotland. The data sets are different from those in 1991, not least because aggregate flow counts are available at the scale of output areas, as well as wards and districts, and because the method of data adjustment to eliminate the risk of disclosure is different from that used in 1991. This paper is in three sections. Firstly, the 2001 interaction data sets are outlined and compared with what was produced in 1991. Work on the re-estimation of 1981 and 1991 data consistent with 2001 geographical boundaries is summarised and the effects of the small cell adjustment method (SCAM) are examined using migration data at three different spatial scales. Secondly, we illustrate the developments of the WICID user interface that have been made to incorporate 2001 data and to add some analytical functionality. Finally, we exemplify the type of analysis that the WICID system can be used to support choosing selected data sets from the 2001 Census.