With the exception of 2001, these data have been created for Vision of Britain by re-districting statistics originally reported for other units. We have also had to deal with variations in the categories and classifications used in statistical reporting over the years.

• 1801-1851:The population statistics come from the table 'Parishes - Area; houses, 1841, 1851; Inhabitants, 1801, 1811, 1821, 1831, 1841, 1851' in Census of Great Britain, 1851. Population tables. I. Numbers of the Inhabitants, in the years 1801, 1811, 1821, 1831, 1841, and 1851., Vol. II. The original 1851 age structure data are for Registration Districts and come from the divisional tables in Volume II, Part II of the 1851 Census Report, Ages, Civil Condition, Occupations, and Birth-Place of the People, BPP 1852-3 LXXXVIII.
• 1861, 1871: At present, we have to use interpolated values for some years as work continues on boundary mapping. These data were interpolated by a simple linear trend applied to the 1851 and 1881 data for total population.
• 1881:These data come from table 2, 'Ages of Males and Females in Registration Districts' in each of the sets of divisional tables in Volume III of the 1881 Census Report, Ages, Condition as to Marriage, Occupations, and Birth Places of the People, BPP 1883 LXXX [C.3722].
• 1911, 1931 and 1951: The original data are for Local Government Districts, so our redistricting will be more accurate than for 1851 and 1881. The 1911 data come from table 8, 'Ages of Persons, Males and Females at each year of age under 21 and in Quinquennial Age-Groups', in Volume VII of the 1911 Census Report, Ages and Condition as to Marriage. The 1931 data come from table 14 and 15, 'Ages (Grouped) by marital condition' in each of the County Reports of the 1931 Census. The 1951 data come from table 21, 'Ages (quinary) by Marital Condition', for County Boroughs and towns over 50,000 population, and from table 22, "Ages (quinary) and Marital Condition', for Rural Districts and smaller towns, in each of the County Reports of the 1951 Census.
• 1901, 1921, 1941, 1961: These data were interpolated by calculating a geometric mean on the populations at the previous and the next census.
• 1971-91: The data are computed from the Small Area Statistics for each year, via the 'Linking Censuses through Time' system. In 1971, the oldest age band available is '75 up'.
• 2001: The data are taken from tables P6, for males, and P7, for females, in the initial release of 2001 census data in September 2002; and from table 2 in Scotland's Census: 2001 Population Report, issued by the GRO(S) again in September 2002.