Purpose and Definition
The concept of a Primary Urban Area was created in an attempt to enable economic and social comparisons between cities using definitions less arbitrary than the administrative boundaries of local authorities, but avoiding one problem of using the Urban Areas defined by the Office for National Statistics - that sprawling conurbations such as the West Yorkshire Urban Area, containing multiple distinct settlements with large degrees of physical and social independence, but that happen to touch, end up being treated as if they were a single city.
To enable this, Primary Urban Areas are defined as being based on areas of continuous built-up land containing urban structures that are within 50 metres of each other, while Urban Areas only require that urban land uses should be less than 200 metres apart.
In addition, to qualify as a Primary Urban Area a built-up area must have a population in excess of 125,000. On this basis England had 56 Primary Urban Areas in 2007.
As Primary Urban Areas were created to allow statistical comparisons, and the majority of statistics are produced based on administrative or electoral geographies, Primary Urban Areas are approximated to local authority and ward level, or to an additional measure called a tract - similar in size to a ward but designed to be subject to fewer revisions over time. It is for these approximate areas that statistics are available. Wards and tracts, being smaller, allow a greater degree of precision in comparing PUAs, but using local authority-based definitions allow PUA comparisons to be made using the wider range of statistics available at this level.
Primary Urban Areas are designed purely as a tool of statistical analysis and aren't intended to form definitive measures of cities for policy purposes. They are named after the largest settlement within them.
Read more about this topic: Primary Urban Area
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