Official statistical manual: unstats.un.org/unsd/demographic-social/Standards-and-Methods/files/Principles_and_Recommendations/Population-and-Housing-Censuses/Series_M67rev3-E.pdf . United Nations, Department of Economic and Social Affairs, Statistics Division; Statistical Papers Series M No67/Rev3. Paragraphs1.4–1.12 define the population census and its reference time, universal coverage and individual enumeration. Paragraph1.5 describes population size, distribution and composition as census benchmarks.