A choropleth chart is a type of data visualization used to represent data on a map, typically by shading or coloring geographic regions, such as countries, states, or municipalities, to indicate variations in data values across different areas. Choropleth charts are a powerful tool for showing spatial patterns and trends in data.
Some key components of choropleth charts include:
- Geographic regions: Choropleth charts display data associated with specific geographic areas. These areas can be countries, states, counties, cities, or any other administrative or spatial division.
- Color coding: Choropleth charts use color coding to represent data values. Each geographic region is shaded or colored based on the value of the data variable being visualized. Typically, a color scale or gradient maps values to colors, with darker or lighter colors representing higher or lower values.
- Data variables: Choropleth charts are suitable for visualizing data variables with a clear spatial component. For example, you can use choropleth charts to show population density, average income, election results, or any other variable that varies across geographical areas.
- Legend: Choropleth charts include a legend that explains the color-coding and helps viewers interpret the map. The legend typically shows the range of data values and the corresponding colors.
- Data aggregation: Data must be aggregated to match the geographic regions on the map. This may involve summing, averaging, or aggregating the data to the appropriate spatial level.
- Interactivity: In interactive choropleth charts, users can often hover over or click on map regions to view detailed information about the data values for that area. Interactive features can enhance user engagement and understanding.
List of recommended resources #
For a broad overview #
This data visualization catalog gives a brief on choropleth maps with illustrations.
What is a Choropleth Map and How To Create One
This blog post by Venngage gives a broad overview of choropleth maps, thier uses, and how to read them.
For in depth understanding #
Cartography: Thematic Map Design
Chapter 6 of this book by Borden D. Dent, Jeffrey S. Torguson, and Thomas W. Hodler focuses particularly on the technique of using choropleth maps for quantitative thematic mapping.
Error on choroplethic maps: definition, measurement, reduction
This essay by George F. Jenks and Fred C. Caspall illustrates how errors in choroplethic mapping inhibit the transfer of information and that there are methods for improving this type of map as a communicative tool.
Case study #
Evaluation of Methods for Classifying Epidemiological Data on Choropleth Maps in Series
This paper by Cynthia A. Brewer and Linda Pickle aims to determine which choropleth classification methods are most suitable for epidemiological rate maps.
James Stewart and Patrick J. Kennelly try to conceptualize the choropleth data as a three-dimensional prism model under simulated illumination, with the height of each enumeration unit a function of its mapped value.
Retrospective Deconstruction of Statistical Maps: A Choropleth Case Study
Marc P. Armstrong and Ningchuan Xiao develop an approach to map deconstruction that enables researchers to investigate the statistical choices made by cartographers by placing each printed map into the universe of all possible choices available to them. Armstrong and Xiao use three published choropleth maps to illustrate their approach.
References #
Data Visualization Resources: Types of Charts and Graphs for Data Viz
