= Population census
A <population census> is the organized enumeration or equivalent statistical accounting of the people in a specified territory at a specified reference time, including selected demographic characteristics. Universality and a common reference time distinguish the target of the count from the days on which information happens to be collected.<Principles and Recommendations for Population and Housing Censuses Revision 3 by the United Nations Statistics Division>[Paragraphs 1.4–1.12]{ref}
For example, if interviews span two weeks, a person born after census night should not silently become part of the census-night population merely because the household is interviewed later. Rules about usual residence also prevent a student or traveler from being counted inconsistently across locations. The resulting counts supply denominators for rates and benchmarks for <statistical sampling>. Attempting complete coverage does not eliminate omission, duplication or classification errors; a census is a measurement procedure, not a guarantee of perfect counts.
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