A census counts the population of a nation, state, or other geographic region. It records information about the population’s characteristics, such as age, sex, and occupation. It may also include data about the region’s agricultural and business sectors. National governments usually conduct censuses every five to 10 years, as recommended by the United Nations.

Census data is commonly used for research, marketing, and planning. For example, population and housing data might determine where schools are constructed or where new bus routes are placed.

In some countries, census data is used to figure out the number of representatives a given community will have in government. In the United States, for example, a county with a large population will have more representatives in state government than a less-populated one.

Historical Censuses

Many early civilizations used census data to determine how their governments would operate. Leaders of ancient Rome depended on censuses to govern their republic and, later, empire. Each male citizen had to appear before the census-takers and account for himself, his family, and his property. The Roman government determined the social position of each citizen by the amount of property he owned. Men with highly prized property enjoyed greater rights and freedoms.

The most well-known historic census appears in the Domesday Book, a survey of England completed in 1086. Scholars say this survey determined the property rights of King William I (William the Conqueror). Assessors recorded how much property and assets—such as cattle and crops—citizens owned, and then taxed them accordingly. William I had conquered England only 20 years earlier. The Domesday Book helped him evaluate what wealth his new kingdom held, and where strategic assets were located.

The Incan Empire conducted perhaps the most unique census of the 15th century. The Incas, whose empire stretched across the Andes mountains, did not have a written language. They recorded information on quipus. A quipuis is a rope made from llama or alpaca hair, or cotton cords. A series of knots on the quipu defined certain numeric and non-numeric values. The Quipucamayocs, or quipu authorities, used these cords to keep track of mita, a form of taxes, and also to run a census of the local population. Quipus recorded the ages, occupations, and wealth of Incan citizens. Some remote Peruvian villages, although very few, still use the quipu system for official local government records.

National Censuses

Today, most national governments conduct censuses for planning purposes. New census-taking technologies and practices have helped governments achieve better results. For example, in 2006, Australia allowed citizens to complete parts of their census online in order to increase participation. In 2011, the country implemented the new Australian Statistical Geography Standard, which allowed census-takers to record more detailed data about populations in limited boundaries, such as postal areas.

Nations organize their census information differently. Criteria are based on factors such as land size, government structure, and economic resources. With about 8.5 million square kilometers (3.3 million square miles) of territory to cover, Brazil records one of the most detailed collections of census data in the world. This collection includes ranked sets of data about the nation of Brazil, major regions, states, municipalities, districts, subdistricts, and neighborhoods.

In 2010, Brazil implemented a number of strategies that aim to increase citizen participation in the census, especially in areas of the country that are hard to reach. Census-takers used handheld computers. These sophisticated computers record and store information on a country-wide broadband internet service. Finally, the handheld computers are able to translate the questionnaire into different indigenous languages, improving the participation of the many indigenous communities in Brazil.

A country’s historical census data shows how the population has changed and gives clues about its history and politics. The censuses of 1911, 1921, and 1931 counted the population by “huts” and not individuals. “Huts” included both individuals and families.

The 1948 and 1959 Ugandan censuses counted individuals, but divided the population between Africans and non-Africans. Uganda was a protectorate of the United Kingdom. Often, ancestry was an indicator of social status, resulting from systemic colonialism and racism. It was important to the government that the census distinguish between those of African, Asian, and European ancestry. After Uganda declared independence in 1962, censuses were taken jointly for people of all ethnicities.

Preparing for and conducting a census requires a lot of time, resources, and labor. The result is large sets of data that tell us about who and what make up our communities, regions, and countries. Ultimately, this data helps political leaders and citizens improve the places in which we live, work, and play.