Between 1995 and 1998 the local authority structure and geography of the United Kingdom was substantially revised. The two-tier system of local government was abolished in Wales, Scotland, and in parts of non-metropolitan England, and replaced with a single-tier system. This involved the creation of a new set of local authority area boundaries which in many places cut across those of the old districts. In addition, many of the local authorities unaffected by the reorganisation nonetheless had experienced small - though demographically significant - boundary changes since the last census. By the time the final phase of the reorganisation came into effect on 1st April 1998 the local government map of the United Kingdom was very different from that of April 1991. There is a need therefore to provide demographic and other geographically based data for the new geography for years prior to 1998. This paper aims to fill a part of this requirement by focusing on two important issues. First, it describes a look-up table detailing exactly how the 1998 local government geography relates to 1991 Census areas, and second, it sets out methods for producing 1991 Census data and mid-1991 population estimates (including single year age detail) for the new geography. A selection of the results produced by the described methods is included in tables and population pyramids
