A national survey run by individual countries, usually once every ten years, to collect information for the purpose of understanding key metrics such as population by area, demographics such as the geographical distribution of age and gender groups, income, dependence on services and infrastructure. In the UK, the census is collected every ten years, the most recent being in 2011. The census is undertaken by the Office of National Statistics in England and Wales, and by its counterpart organisations in Scotland and Northern Ireland.