A census is a count of the population of a nation, state, city, or other geographic region. It records information about the population's characteristics, such as age, sex, and occupation. It may also gather data about the region's agricultural and business sectors. National governments usually take censuses every five to 10 years.

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

In some countries, census data is used to figure out the number of representatives each community will have in government. In the United States, for example, a county with a large population will have more representatives in the state government than a less-populated one. The same is true at the national level. States with a large population are given more seats in the House of Representatives, one of the two chambers of Congress.

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. Officials recorded how much property and assets—such as cattle and crops—citizens owned. Then, citizens were taxed at a rate based on the recorded information. Scholars say this survey also determined the property rights of King William I. William, known as William the Conqueror, had conquered England only 20 years earlier. The Domesday Book helped him evaluate what wealth his new kingdom held. It also revealed where militarily important 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 quipu is a rope made from llama or alpaca hair, or cotton cords. A series of knots on the quipu represented various numbers, as well as other information. 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 take censuses for planning purposes. Censuses consist of a series of questions, which citizens answer by filling out a form or by speaking with a census-taker.

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 introduced the new Australian Statistical Geography Standard. It allows census-takers to record more detailed data about populations within limited boundaries, such as postal areas.

Nations organize their census information differently. Brazil, which has about 8.5 million square kilometers (3.3 million square miles) of territory, records one of the most detailed collections of census data in the world. It includes data about the nation of Brazil, major regions, states, municipalities, districts, subdistricts, and neighborhoods.

In 2010, Brazil introduced new technology it hopes will increase citizen participation in the census, especially in hard-to-reach areas of the country. Census-takers now use handheld computers. These record and store information on a country-wide broadband internet service. The handheld computers are also able to translate questions into different indigenous, or native, languages.

A country's historical census data can provide clues about its history and politics. For example, the 1948 and 1959 censuses in Uganda divided the population between Africans and non-Africans. Uganda was then a protectorate controlled by the United Kingdom. It was important to the British-controlled Ugandan government that the census distinguish between those of African, Asian, and European ancestry. Often, a person's ancestry was an indicator of their social status, or rank, in Ugandan society. This was the result of colonialism and systemic racism. After Uganda declared independence in 1962, censuses no longer separated out ethnicities in the same way.

Censuses require a great deal of time and resources, as well as a large workforce. Yet, they are very much worth the effort. Censuses provide large sets of data that tell us 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.