ABSTRACT
The 1 99 1 Census of population was the first in the UK to be conducted in what might be called the ' GIS era ' . Despite the fact that GIS use in socio-economic applications had been widespread since the mid-1 980s (Martin, 1 996) , the dcsign of a single census geography based on enumeration districts (EDs) for England and Wales was undertaken manually, resulting in the production of a large number of paper maps. Digital boundaries were subsequently crcatcd commercially by digitizing maps provided by the Office for Population Censuses and Surveys (OPCS), and the ED9 1 and ED-line products produced in lhis way have seen extensive commerciaL governmental and academic use both for simple thematic mapping and more complex GIS applications 1 993; Charlton et al. , 1 995) . The government committee on the handling of geographic information in 1 987 strongly endorsed the use of postcodes as the basis for census geography design (DoE, 1 987) . However, the 1 99 1 geography was based cntirely on census-specific EDs, which have no clear relationship with postcodes, except in a very few local authorities , despite the widespread use of postcode geography in other applications (Raper et at. , 1 992). The manually-designed geography of 1991 continued to incorporate wide variation in ED populations, including the presence of sub-threshold EDs, whose small populations caused them to be merged with neighbouring areas in order to preserve confidentiality. To commentators such as Openshaw ( 1995), the continued use of enumeration geography for data output, the lack of an integrated digital geography and the general ' neglect of GIS ' in 1 99 1 are seen as unacceptable.
