https://thenextweb.com/syndication/2018/07/29/prepare-yourself-facebook-could-be-the-future-of-national-census/

Every ten years, governments around the world conduct their national census: a count of the resident population. This is no easy task. The 2011 Chinese census, for instance, was a vast operation relying on six million enumerators taking census questionnaires from door to door. Knowledge of a population’s composition is crucial for government planning, for example in terms of investing resources in elderly care. In some countries, it is the basis for dividing parliamentary seats over electoral districts.

Historically, census counts have been relevant to the development of modern nation states because they link populations to a territory. They have also been key to the governance of colonial populations by, among other things, introducing and reinforcing hierarchies of ethnicity, race and class.