How the Census Works

Technology and the Census
Census Bureau employees review punch cards containing data from the 1940 census. U.S. Census Bureau

Census taking became more streamlined in 1880 when trained workers were employed for the first time. Technology followed in 1890. The Census Bureau developed a new electrical machine that could add up responses to questions after census workers punched holes in the right places for each answer. Cards were then fed into a machine that totaled the result [source: U.S. Census Bureau]. It was bulky but a great advance at that time — anything that sped up the process was a help since some of the results have to be ready nine months after Census Day (more about that later).

The first modern computer, called ENIAC, was completed in 1946 at the University of Pennsylvania. This computer, which was really many machines working together, took up a whole room. The system was ready in time for use in parts of the 1950 census, and the Census Bureau ordered its own computer, called UNIVAC. This was the first successfully used civilian computer. Data was input using magnetic tape as well as via punch cards. That technology has advanced over the years and now high-speed supercomputers assist with the census [source: U.S. Census Bureau].

The major technological leap for the 2010 census was the use of handheld GPS devices to update the Census Bureau's master address list of the nation's 145 million residences. The accuracy of GPS coordinates allowed the bureau to correctly assign each home, apartment or trailer to its appropriate Congressional district. In the past, armed only with paper maps, census workers accidentally assigned an average of 5 percent of American residences — particularly rural homes — to the wrong district. With the upgrade to GPS devices, the bureau projected a 0.5 percent error rate [source: Luhby].

The biggest technological upgrade for 2020 is that it will be the very first census that can be completed online. Most U.S. households will receive a mailed invitation in March 2020 to go online and complete the census. Only households that fail to complete the census by early April will receive a paper questionnaire [source: U.S. Census Bureau]. The hope is that the online census will improve response rates and lower the cost of sending census workers to follow up.

Another cost-cutting technology debuting in 2020 is the use of satellite imagery to locate new homes and identify those that no longer exist. In the past, census workers had to physically canvas all urban rural locations to verify addresses. Now many of the farthest-flung locations can be checked remotely by comparing old and new satellite images. The move to satellite verification is expected to reduce the canvassing workforce from 150,000 workers in 2010 to only 60,000 in 2020, a good move at a time of low unemployment [source: CBS News].

Most of the U.S. census was taken door-to-door until 1960, when census officials recognized the inefficiency of this method in dealing with such a fast-growing, mobile population. That's when they decided to use the mail to distribute forms. In the 2010 census, 74 percent of households returned their census forms by mail, and the remaining households were counted by an army of census workers [source: U.S. Census Bureau].