Geospatial Data from the US Census Bureau
Demographic data is "the statistical characteristics of human populations (such as age or income)." Etymologically, the word is a combination of the Greek words dêmos (people) and graphein (write) - literally, writing about people (Merriam-Webster 2020). Typical demographic variables for an area include:
- Median Household Income
- Median Age
- Median Family Size
- Percent of Residents With a College Degree
- Percent of Residents That Were Born Outside the USA
- Percent of Residents That Are Military Veterans
The US Census Bureau (USCB) is the part of the US federal government responsible for collecting data about people and the economy in the United States. The Census Bureau has its roots in Article I, section 2 of the US Constitution, which mandates an enumeration of the entire US population every ten years (the decennial census) in order to set the number of members from each state in the House of Representatives and Electoral College (USCB 2017).
The American Community Survey
Among the Census Bureau's many programs is the American Community Survey (ACS), an ongoing survey that provides information on an annual basis about people in the United States beyond the basic information collected in the decennial census. The ACS is commonly used by a wide variety of researchers when they need information about the general public.
Unlike the constitutionally-mandated decennial census which is only taken every ten years, the ACS continuously surveys people in America's communities so that the ACS data can be more detailed and current than the decennial census. However, because the ACS is a survey rather than a complete count like the decennial census, there is uncertainty about how accurately the sampling represents the facts on the ground, and that uncertainty is expressed in a statistical margin of error (MOE) on most ACS values (US Census Bureau 2018).
In order to preserve the confidentiality of respondents (and the associated willingness of people to respond to highly-personal questions), the US Census Bureau generally only releases data that has been aggregated into areas at various geographic scales:
- Core-Based Statistical Areas (Metropolitan Areas)
- Places (Incorporated Cities and Unincorporated Communities)
- ZIP Codes
- Census Tracts
Although ACS data is captured through surveys that are administered on an ongoing basis, ACS data is released annually in aggregation by two different time-periods:
|One-Year Interval||Five-Year Interval|
|Useful when you need the most current data about an characteristic that changes frequently||Useful when you need the most accurate data about a characteristic that stays fairly stable over time|
|Useful for areas that are changing rapidly||Useful for areas that are well-established|
|Often has gaps in sparsely-populated rural areas||Data is more complete|
|Based on fewer surveys, so it has wider margins of error||Based on more surveys, so it has lower margins of error|
Community Profile Pages
If you are looking for quick information on a specific state, county, city or community, the USCB provides profile pages in data.census.gov that include basic demographic information about population, income, education, etc.
You can access a profile page by typing the name of the area of interest into the search bar and waiting for it to autocomplete. If there is a profile page, a link to that page will appear for you to select.
For areas that do not have profile pages (like ZIP Codes), searching the portal will give you links to tables where you can find information on that area.
Downloading Table Data
Data from a variety of different programs is available on data.census.gov, and data from each program is sliced and diced across a variety of different tables.
Three ACS tables containing useful groups of data include:
- DP02 Selected Social Characteristics in the United States
- DP03 Selected Economic Characteristics in the United States
- DP04 Selected Housing Characteristics
The video below shows how to download the DP03 (Selected Economic Characteristics) table with county-level data for Illinois from data.census.gov.
- From the data.census.gov home page, search for DP03. The default table shows values for the entire USA.
- Click Customize Table.
- Click Geos to select the type of geographic area. For this example, we will use County, within Illinois, and All counties in Illinois.
- Close to update the displayed table.
- Click Download, make sure the correct data set is selected and that the File Type is CSV.
- Select the appropriate Product if needed. For this example we will use the most recent five-year estimates so that data is available for all areas.
- Save the .zip file to your local computer.
- Create a working directory for your data and script.
- Open the .zip archive, copy the file with a name containing the word "data" in it, and paste it into your working directory.
- If you wish to inspect the data table and see what is in it, you can open it in a spreadsheet program.
Mapping Table Data
US Census Bureau data is commonly used to create maps, although the process of mapping a table will require additional processing that depends on the software used to create the map.
The following tutorials offer some guidance: