Districts: The county of Somerset is divided into five Districts: Mendip, Sedgemoor, South Somerset, Taunton Deane and West Somerset.
Wards: Each District contains a number of electoral Wards, which are the areas represented by members elected to the District Councils. The boundaries change periodically to reflect population numbers within the wards ensuring even numbers for voting. In Somerset, a number of changes were made in 2007, primarily affecting Mendip District. Because of the different ways by which the 2001 Wards (144 in total) and 2007 Wards (142) are defined, not all data are available for both types of Ward. You may also come across data for 2003 ST Wards. These are identical to the 2001 Wards except for a small number of Wards in West Somerset. Here, three pairs of 2001 Wards with relatively low numbers of people have been merged to make the resulting areas more robust for analysis.
Electoral Divisions: These are the areas (currently 58) represented by members elected to Somerset County Council. As with Wards, each is wholly contained within a District but Ward boundaries do not necessarily fit within an Electoral Division.
Parishes: Somerset is divided into 329 civil parishes, which originally arose from Church of England boundaries. They range from the very small (communities of around 50 people) to the very large (for example, the whole of Bridgwater). In addition, much of Taunton is classified as Unparished.
Lower Super Output Areas (LSOA) and Middle Super Output Areas (MSOA): Parish, Electoral Ward, District and County boundaries change over time. In 2001 following the Census, the Office for National Statistics (ONS) created its own boundary system so areas could be compared consistently over time. The smallest geographic areas are known as Output Areas (OA). OAs fit into Lower Super Output Areas (LSOA), which in turn fit into larger geographic areas Middle Layer Super Output Areas (MSOA). In 2001 throughout the UK each of the LSOAs contained around 1,500 people and the MSOAs around 7,500 people. In Somerset, there are 327 LSOAs and 71 MSOAs.
Postcodes: The postcode system introduced by the Royal Mail uses boundaries which are not aligned with those used by administrative areas or the ONS. Consequently, where data are available only at postcode level they can be aggregated to any other geographical boundaries, where appropriate.