Output geography is a geographical division of the enumerated area to which the census results are aggregated. In the past, the collection geography has been used as the output geography, for example, in 1991 the enumeration districts (i.e. the collection geography) of England and Wales were used as output geography and in 1971 the results were tabulated for both EDs (collection geography) and regular grid squares. In 1981, smaller units called Output Areas (OAs) were introduced in Scotland and are also to be used for the publication of census results in England, Wales and Northern Ireland for the 2001 Census
Whichever geography is used for the output of Census results, the important prerequisite is that it should nest within the statutory geography of the country in force at the time of the census. This ensures that the population characteristics at administrative and political level can be monitored. In practise, ED's are designed to nest within wards (the smallest statutory area) and aggregated census results are then produced for the full hierarchy of administrative divisions above this.
More information on output geography can be found in Rees and Martin, 2002