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Visualizing changes in population using binary FRED maps

Our FRED graphs and maps can be customized to allow you to tell the story behind the numbers. In an earlier post, we described the differences between using fractile and equal interval data legends. Today we use those customization options to create binary maps.

A binary map is a data visualization format where the range of data is sorted into two categories. The FRED map above uses that format to color the states where population increased between 2021 and 2022 (the darker areas) and where it decreased (the lighter areas). The data are reported by the US Census Bureau; in addition to conducting its decennial census, it also provides annual population counts for states and counties.

The map shows many states, including Texas, Florida, and North Carolina, that gained residents and several states, including New York, California, and Illinois, that lost residents. However, for all but three states, these population changes were unevenly distributed within the state. To show that, we can tap into the same US Census data, but at the county level.

Our second FRED graph uses the same binary format described above to identify population changes between 2021 and 2022 in each county. Notice that in every state where overall population decreased, there is at least one county where population grew. Similarly, in almost all states where overall population increased, at least one county lost residents. Only in Maine, New Hampshire, Delaware, and the District of Columbia did population increase in all counties or county-equivalent areas.*

Let’s wrap up with one reflection on the data visualizations we created. The binary maps are best suited to easily show the prevalence of increases and decreases in population across regions; they don’t allow us to visually compare the magnitude of those changes. For example, while Vermont gained 92 residents and Arizona gained slightly more than 94,000, both state areas are shaded the same color. But, if we’re interested in visually comparing data ranges using a map, FRED’s default of five fractile data intervals is a reliable starting point.

*In this dataset, the District of Columbia is a single county.

How these binary maps were created: Search FRED for “Resident Population by State” and select any of the states listed. Click the “View Map” option. Click “Edit Map” and change the units to “Change, Thousands of Persons”. Next, under “Format,” change the “Number of color groups” to 2 and “Data grouped by” to “User Defined Method.” Change the interval values to 0 for the first entry. Last, click on the colored boxes to customize the colors for each data interval.

Suggested by Patrick Wade and Diego Mendez-Carbajo.

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