Using Maps to Compare Data across Regions

Choropleth maps are maps that use a scale of colors to indicate numerical values for different geographical areas. Such maps are helpful in getting a visual comparison of data across regions. For example, a choropleth map could use colors to show how the unemployment rate varies among the 50 U.S. states.

St. Louis Fed online economic database FRED has over 800,000 time series. More than half of those series can be visualized through maps, Diego Mendez-Carbajo noted in a recent Page One Economics essay. We can use FRED maps to examine data series across nations, U.S. states, U.S. counties, U.S. metropolitan statistical areas and more. In this blog post, I use FRED’s map feature to look at four geographic data sets in the U.S., ranging from GDP to the poverty rate.

When examining the FRED maps below, you can hover over regions or refer to a key in the bottom right corner for values.

GDP by County

Gross domestic product (GDP) is a gauge of the size of an economy. It measures the total market value of all final goods and services produced over a period, typically a year.

Below is a map showing the GDP of U.S. counties in 2021 as calculated by the Bureau of Economic Analysis. Notably, places with larger populations also tend to have a higher GDP, because there are more workers to contribute to the economy. Therefore, it is important to be aware of population when comparing the GDP of different regions.

Median Household Income by County

The Census Bureau provides estimates of income and poverty statistics for school districts, counties and states through its Small Area Income and Poverty Estimates (SAIPE) program.

“The main objective of this program is to provide estimates of income and poverty for the administration of federal programs and the allocation of federal funds to local jurisdictions,” according to the Census Bureau website.

The estimates for median household income are based on income for all members in a household who are 15 years old or older. Below is a map showing the median household income by county for 2021.

Poverty Rate by County

The poverty rate can be an important indicator of a population’s economic outcomes. FRED includes estimates of poverty rates through the Census Bureau’s SAIPE program.

“The Census Bureau uses a set of money income thresholds that vary by family size and composition to determine who is in poverty,” according to the Census Bureau website. These thresholds don’t change based on location. If the total income of a family sharing a household is below the threshold, members of the family are included in the poverty rate.

The Social Security Administration developed these thresholds in the mid-1960s by calculating “the cost of a minimum food diet multiplied by three to account for other family expenses.” The Census Bureau updates the thresholds to adjust for inflation using the consumer price index from the Bureau of Labor Statistics (BLS).

The FRED map below examines the poverty rate by county for 2021.

Median Listing Price by State

Housing is typically the largest expense for households. The average “consumer unit,” or household, spent $22,624, one-third of its total expenditures, on housing in 2021, according to calculations based on the BLS’ Consumer Expenditure Surveys data.

Realtor.com aggregates the prices of houses listed for sale on its site and releases monthly data on, for instance, the median listing price for single-family and multifamily homes, as shown by state for June 2023 in the map below. (If you want to see the median listing price per square foot by state, check out this FRED map.)

Median listing price can be an important indicator for those who are in the market for purchasing a home. However, it is less helpful for those who are in the rental market.

Next time you’re examining a data series in FRED, look to see if there’s a green button in the top right corner that reads “VIEW MAP.” If the button is there, you can click on it to see how that data series compares across geographic regions.