Census basics

What is Census?

Census is the procedure of systematically acquiring and recording information about every resident in the United States mandated by Article I, Section 2 of the Constitution. It takes place every 10 years, and the latest census was held April 1, 2010. It is the most complete source of information about the population. 

Which geographies is the data collected for?

The Census Bureau releases demographic data about the country at a variety of different geographic levels. Some of these geographies, such as states, congressional districts, or zip codes, are familiar to most users of the data. Others, such as census tracts and block groups, are specialized divisions created by the government specifically for the purposes of census enumeration. 

The basic hierarchical organization of census geography is Nation > States > Counties > County Sub-Divisions > Census Tracts > Block Groups > Blocks, with each level nested completely within its predecessor.

These levels cover all areas in the United States, and added up, their populations equal the entire population of the United States. Other levels, such as places, can cross the boundaries of other levels, and some, such as ZIP codes, do not cover all areas of the United States. ZIP codes only cover those where mail is delivered.

What is the data used for?

The data collected by the decennial census determine the number of seats each state has in the U.S. House of Representatives and is also used to distribute billions in federal funds to local communities. The information the census provides also allows central and local government, health authorities and many other organisations to target their resources more effectively and to plan housing, education, health and transport services for years to come. Census data are used extensively in marketing applications, supplementing smaller surveys, cooking up estimate and projection numbers, helping scholarly researchers learn more about residents and neighborhoods and many other uses.