Planning for the 1991 CensusAuthor(s): Steve WiseSource: Area, Vol. 21, No. 3 (Sep., 1989), pp. 313-315Published by: The Royal Geographical Society (with the Institute of British Geographers)Stable URL: http://www.jstor.org/stable/20002763 .

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Observations 313

boundaries shown in Figure 1 are Post Office copyright-postcode maps may be obtained from Postcode Marketing Section, Post Office Marketing Dept., 22-25 Finsbury Square, London EC2A IPH.

References Wise S M and Pellatt R P (1987) Rapid access to a large cartographic database using CAFS: a feasibility

study. Wales and South West Regional Research Laboraory Technical Report 4, Dept of Town Planning, UWCC, Cardiff.

Wise S M (1988) 'Using Contents Addressable Filestore for rapid access to a large cartographic data set',

International_ournal of Geographic Information Systems 2, 111-20.

Planning for the 1991 census Steve Wise, SWURCC, University of Bath, Claverton Down, Bath BA2 7AY

Although the next census is still over 2 years away planning for it in fact started two or three years ago. Things are now beginning to gather momentum, with the publication of a Government White Paper formally announcing plans for the 1991 census, and this seems a good opportunity to summarise the current state of play. Firstly though for those who may not be familiar with it, a brief resume of what happened for the 1981 census.

The body responsible for the census is the Office of Population Censuses and Surveys (OPCS), who plan the whole exercise of collecting, analysing and publishing the data. The form itself must be designed to be as simple as possible to complete, and to provide information which will be useful to central government, local government, health authorities and academics. On census night, the forms are collected by enumera tors each of whom covers a small area called an enumeration district (ED). The EDs are drawn up so that they lie within electoral wards-these in turn nest into districts which nest into counties giving a hierarchy of areas covering the country.

It is part of the law governing the census that no data relating to a single individual can be disclosed by OPCS, so all statistics produced from the forms must be some form of summary. The most popular set of statistics are what are called the Small Area Statistics or SAS. For each ED OPCS calculate a series of cross-tabulations-age distribution by sex, numbers in employment by age, etc. In all the 1981 SAS contained 53 tables, amounting to over 5500 counts (or cells). Because of the hierarchical nature of the areas, using the ED SAS it is possible to calculate figures for wards, districts and counties.

The SAS are published in printed form, but since 1961 have also been available on magnetic tape. The early problems were the large volumes of data and the lack of any suitable software for dealing with them. Some users did write their own software, but for the 1981 data the academic sector collaborated with local authorities to produce the SASPAC package specifically for dealing with SAS. The package was distributed by LAMSAC, a body funded by local authorities to coordinate activity in (inter alia) computing in local government.

The 1981 SAS were bought by the Economic and Social Research Council (ESRC) and placed in the ESRC Data Archive at Essex. From here they were distributed to a number of university computer centres where SASPAC was also installed-the sites included ULCC, UMRCC, SWURCC, ERCC, NUMAC and Aberdeen. Representa tives from these sites and from the Archive formed a Working Party under the auspices of the Inter-University Software Committee (IUSC). The working party later nego tiated the purchase of digitised ward boundaries for use in producing maps using the data.

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314 Observations

So what of 1991?

OPCS have been planning for 1991 for quite some time, and a White Paper has recently been produced outlining their plans. LAMSAC and the universities have been involved in the discussions involved in this process; within the academic sector two groups have played a major role: (a) The IUSC Datasets Working Party established to deal with the 1981 data. The

main interests of this group are the dissemination of the data to users and software for accessing it.

(b) ESRC have set up a committee, chaired by Prof. Neil Wrigley. Their main interests are in the topic content of the census and in census geography. They have undertaken a survey of academic census data users, the findings of which were recently published (Marsh 1988).

However it is fair to say that both groups take a broad interest in the whole issue of the 1991 census.

Some of the areas of current discussion are:

(1) The data

There are several issues relating to the actual census data. Previously the only way to ensure confidentiality was by producing tabulated summary statistics however this

means that OPCS must decide beforehand on suitable areas for which to calculate the tables, and on suitable class intervals for the variables. Both these can cause problems later especially when comparing census data with other data collected for different areal units or tabulated with different class intervals.

There has been a great deal of interest in the idea of using post-codes as the basic areal unit (this is already the case in Scotland in fact). Unit postcodes are small (containing roughly 15 houses on average); too small in fact for SAS to be based on individual unit postcodes, but by combining data for different postcodes OPCS could approximate other areas such as wards, parishes, school catchment areas etc. A further advantage is that other data such as health records, are already postcoded, so it would

make it easier to combine this with census data. OPCS originally proposed to draw boundaries around all the unit postcodes (which are simply defined as lists of addresses) and then digitise these. These could then be used in planning the EDs to be used on census night as well as in producing the SAS. However this plan foundered for reasons of cost-OPCS are now proposing to ensure that each census form has a valid postcode, so that it should be possible to offer SAS based on postcode areas in addition to the usual ED and ward base.

Two other more radical alternatives to SAS are also being discussed. These are summarised here but are explained at greater length in issues 39 and 40 of the ESRC

Data Archive Bulletin. (a) Public use microdata sample: many other countries release a sample of their census

data on an individual basis. Naturally steps are taken to ensure that the data are

anonymous and the identity of the original individuals cannot be derived. A recent survey of academics by the ESRC committee showed there was strong support for a public use microdata sample from the 1991 census, and OPCS appear to be

seriously considering this as an addition to SAS. (b) Customer selected tables: Prof David Rhind of Birkbeck is working on a prototype

system to allow a user to produce his/her own Small Area tables. The prototype system used ICL INDEPOL database software, but is currently being ported to

Model 204 at UMRCC. The database contains the original personal records de rived from Italian census forms (the Italian census has much in common with the

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Observations 315

British one). From these, the user can request tables for selected areas, with a free hand in choosing which variables to tabulate and which class intervals to use. The security features of the database software are used to ensure that a user cannot extract an individual record from the database.

(2) Software The sort of software which is suitable for accessing the data depends partly on the format in which the data are made available of course-a public use sample can be analysed with the sort of software usually used for handling survey data, and the customer selected tables are based upon a suitable database package. However it seems likely that SAS will be released much as in 1981, and LAMSAC have been making plans for designing the successor to SASPAC-this seems likely to be an improved version of the current product with one or two new features.

A lot of interest has also been focussed on the use of micros for analysing census data. Increasingly users are using SASPAC on a mainframe to extract a subset of census data, and then transferring this to their micro for subsequent analysis, mapping, etc. This is clearly going to be increasingly attractive, and there is some interest in developing software to make this process much easier for the user.

Another development in the area of micros is the possibility of storing the census data on CD-ROM, which means the whole process of extracting particular parts of the data and analysing them can be done on the micro. This has already been done for the Australian census, and OPCS have commissioned a pilot study using 1981 GB data. In terms of software it is still early days; the data will not be available until 1993 or so, and given the speed of development in hardware and software, this is a long way away. The only thing which can be said for certain is that there are likely to be more options open to the census user than there were in 1983.

(3) Census mapping

Another development since 1981 has been the growth in popularity of producing maps using census data. Several PC packages now allow census maps to be produced very easily (SPSS-PC and Atlas* Graphics for example). More recently there has been a growing interest in Geographical Information Systems (GIS). Using GIS software it is possible to do much more than simply map census data; a good GIS gives a user a graphical interface to analysing the data and combining it with other data. All these applications require the boundaries of the census area (EDs, wards, etc) to be digitised.

For 1981 only the wards were digitised on a national scale, although several local authorities digitised the EDs for their own areas. Both OPCS and LAMSAC have accepted the importance of having a set of digitised boundaries, and although it is not clear who will do the work or what the cost will be, it seems likely that there will be a set of digitised boundaries in time for 1993.

In this article I have attempted to cover a lot of ground very quickly. Anyone who would like to find out more about any particular aspect of 1991 census planning is invited to contact the author at SWURCC or census support staff at one of the other sites holding the 1981 data.

References Marsh C, Arber S, Wrigley N, Bulmer M and Rhind D (1988) 'The views of academic social scientists on the

1991 census' Environment and Planning A, 20, 851-89

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