How to create a choropleth map
What is it for?
Choropleth maps are thematic maps in which areas (such as states, boroughs and regions) are shaded or patterned according to your data.
Creating a choropleth map can be very useful if you need to:
- Visualize data in a predetermined geographic area;
- Display a value’s distribution/variability across a region.
How to get started
TIP: We recommend using numerical values or geocodes to merge your data, as names can often be spelled differently in various databases. Codes are more likely to be consistent across data, and will therefore merge more successfully in the template.
Customizing your choropleth map
After importing your data, you can then focus on customizing your visualization. The shading of the map will depend on whether your values are categorical or numeric.
Numerical data usually refers to data that displays some numeric relationship, for example, temperature variations, population numbers, or percentages. On the other hand, categorical data usually represents data that can be split into groups, such as race, gender, or election results.
Flourish sets the default scale type as categorical, however, you can change this by opening the Regions layer settings and switching to Numeric instead.
By choosing the Numeric scale type, you can also select a sequential or diverging legend, as well as choosing a linear or binned coloring.
- A sequential palette ranges between two colors (typically having one “main” color) ranging from white or a lighter shade to a darker one, by varying one or more of the parameters in the HSV/HSL color space.
- A diverging palette ranges between three or more colors, usually between two contrasting colors at either end with a neutral color or white in the middle separating the two. Diverging palettes should only be used when there is a value of importance around which the data are to be compared. This could be to mark whether something is positive or negative, for example.
In addition, when using binned or linear coloring, you can manually set bins or thresholds for your colors and your legend. Learn more about this here.