Population size and density

The United Nations Statistics Division is the primary agency responsible at the international level for collecting official national statistics related to population size and density. These have been collected and disseminated on an annual basis through the Demographic Yearbook system since 1948.

More specifically, the following information are gathered:

Total population

Population by

  • age and sex
  • geographic areas (urban/rural, major geographic areas, cities with 100 000 population)
  • marital status
  • ethnocultural characteristics (i.e., national or ethnic origin, religion and language)
  • size and type of nuclear family
  • size and type of household

Other agencies or organizations that deal with population size and structure include

United Nations Population Division prepares United Nations estimates and projections of population by age and sex for countries and areas of the world. These estimates and projections are based on national data provided by the United Nations Statistics Division. The latest estimates and projections of population size are published in the World Population Prospects. The Division also uses data on population density and urbanization as input for estimating urbanization. Those estimates are presented in World Urbanization Prospects.

United Nations Human Settlements Programme (UN-HABITAT) looks at urbanization from a different angle. It collects, collates, analyses and reports data on national, urban/rural and city level in order to monitor human settlement conditions and trends.

United Nations Permanent Forum on Indigenous Issues, in collaboration with the United Nations Statistics Division, review national practices of collecting and disseminating data on national and/or ethnic group, language and religion with special focus on indigenous persons.

Demographic Yearbook - Statistics

Standards and methods

The United Nations Statistics Division issues standards and methods approved by the Statistical Commission to assist national statistical authorities and other producers of statistics in the collection, compilation and dissemination of data.

Principles and Recommendations for Population and Housing Censuses, Revision 2

Concepts and definitions

Source: Principles and Recommendations for Population and Housing Censuses, Rev 1

A. Total population (paras. 2.42.- 2.48.)

For census purposes, the total population of the country consists of all the persons falling within the scope of the census. In the broadest sense, the total may comprise either all usual residents of the country or all persons present in the country at the time of the census. The total of all usual residents is generally referred to as the de jure population and the total of all persons present as the de facto population.

In practice, however, countries do not usually achieve either type of count, because one or another group of the population is included or excluded, depending on national circumstances, despite the fact that the general term used to describe the total might imply a treatment opposite to the one given any of these groups. It is recommended, therefore, that each country describe in detail the figure accepted officially as the total, rather than simply label it as de jure or de facto.

The description should show clearly whether each group listed below was or was not counted in the total. If the group was enumerated, its magnitude should be given; if it was not enumerated, an estimate of its size should be given, if possible. If any group is not represented at all in the population, this fact should be stated and the magnitude of the group should be shown as "zero". This may occur particularly with groups (a),(b), (d ) and (n) described below.

The groups to be considered are:

  • (a) Nomads;
  • (b) Persons living in areas to which access is difficult;
  • (c) Military, naval and diplomatic personnel and their families located outside the country;
  • (d) Merchant seamen and fishermen resident in the country but at sea at the time of the census (including those who have no place of residence other than their quarters aboard ship);
  • (e) Civilian residents temporarily in another country as seasonal workers;
  • (f) Civilian residents who cross a frontier daily to work in another country;
  • (g) Civilian residents other than those in groups (c), (e) or (f) who are working in another country;
  • (h) Civilian residents other than those in groups (c), (d), (e) (f) or (g) who are temporarily absent from the country;
  • (i) Foreign military, naval and diplomatic personnel and their families located in the country;
  • (j) Civilian foreigners temporarily in the country as seasonal workers;
  • (k) Civilian foreigners who cross a frontier daily to work in the country;
  • (l) Civilian foreigners other than those in groups (i), (j) or (k) who are working in the country;
  • (m) Civilian foreigners other than those in groups (i), (j), (k) or (l) who are in the country temporarily, including refugees;
  • (n) Transients on ships in harbour at the time of the census.

In the case of groups (h) and (m), it is recommended that an indication be given of the criteria used in determining that presence in, or absence from, the country is temporary.

In those countries where the total population figure has been corrected for underenumeration or overenumeration, both the enumerated figure and the estimated corrected populationfigure should be shown and described. The detailed tabulations will of necessity be based only on the actual enumerated population.

B. Sex (para. 131.)

Sex is a basic characteristic needed to describe a newborn child, a decedent or a foetal death. Data should be categorized into "male" and "female", and in case of a foetal death, the category "unknown" is also appropriate.

Age (paras. 121.- 129.)

Age is the interval of time between the day, month and year of birth and the day, month and year of occurrence of the event, expressed in the largest completed unit of solar time, such as years for adults and children, and months, weeks, days, hours or minutes of life, as appropriate, for infants under one year of age. Every effort should be made to ascertain the precise age of each person.

Information on age may be secured either by obtaining the year, month, day and hour of birth or by asking directly for "age at the last birthday". The first method usually yields more precise information but may be difficult to use in the case of illiterate respondents. Additional data processing is necessary to convert “year-month-day of birth” into “completed years of age”, but the results are usually more accurate provided that the exact date of birth is known to the respondent.

The direct question on age at last birthday is more economical to process but may yield less precise results since it more easily permits approximate replies, including preferences for even-numbered ages and those with the terminal digit "0" or "5". It is, however, the appropriate question to use when a considerable proportion of the population cannot give a precise birth date. Thus, it may be seen that "age" is a derived topic when calculated from the topic "date of birth" but is a direct topic when “date of birth” is not obtained (see date of birth (topic 14)).

Where exact age is unknown, estimated age may be recorded. To help arrive at a reasonable estimate of age among less literate persons, it may be useful to employ a historical calendar consisting of a list of dates of well-known events such as famines; epidemics; natural disasters, such as eruption of volcanoes or earthquakes; construction of landmarks, dams and bridges; imposition of new taxes or regulations; or significant political changes. Climatic and farming cycles, and religious or national festivals may also be used. Estimation of the age of an individual may also be attempted by employment of simple criteria of physiological age or by reference to the ages of other members of the household having a known relationship to the person whose age is being estimated.

Obtaining relatively reliable information on age calls for special efforts on the part of the interviewer (the registrar, the physician, the marriage officiant etc.). Care must be exercised, for example, in those cultures where age is reckoned from the New Year. In such communities, an infant is considered to be one year old at birth and to become two years old at the succeeding New Year (it may be Chinese or Moslem), and then to continue to advance one year at each successive New Year, regardless of actual birth date. Thus, unless special care is taken to ask for date of birth in terms of the solar calendar, reports on age for persons following this custom are likely to result in an upward bias averaging about one and a half years. Information on age of mother and father for live births and foetal deaths should be collected in such a way as to permit classification into five-year age groups between 15 and 49, with terminal groups of "under 15 years" and "50 years and over".


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