Use Dorling cartograms instead of rectangular cartograms for big-picture pattern summary
For overview tasks on geospatial cartograms, prefer a Dorling cartogram type on area-encoded map views to improve insight and mitigate broad-pattern reading errors for readers summarizing spatial trends and distributions.
- purpose:refine
- basis:empirical
- chart:map
- data:geospatial
- quality:insight:use
- lever:chart-family
- reading-mode:overview
- channel:area
advice
Choose a Dorling cartogram for the big picture
Use a Dorling cartogram when the chart’s job is to show the overall pattern rather than detailed map reading. For example, replace a rectangular cartogram with a Dorling cartogram for summarize-the-pattern tasks about broad spatial distributions or trends.
reason
Why Dorling cartograms help overview reading
Simple circular marks make the overall pattern easier to scan, while heavily schematic rectangular regions interfere with reading the big picture.
Mechanism: A Dorling cartogram reduces the visual complexity of the map to circles sized by value, which helps readers summarize broad spatial patterns without getting distracted by distorted polygon geometry.
Evidence: In the controlled study, Dorling cartograms ranked best on summarize accuracy and were significantly more accurate than rectangular cartograms, which performed worst for the big-picture task (Nusrat et al., 2018; Zeng & Battle, 2023).
context
Use when overview matters more than detailed map reading
- User Goal: Summarize overall patterns, trends, or distributions across regions.
- Task: Read the big picture from a cartogram rather than inspect exact local relationships.
- Data: Geospatial regions with values encoded by size.
- Chart Setting: A static summary view where the map is used to communicate broad spatial structure.
- Success Criterion: Better pattern-summary accuracy.
exceptions
Do not use when detailed geography is part of the task
Break it when: Geographic locations and adjacencies are important and readers need detailed map reading. Why: Dorling cartograms do not preserve shape or topology well enough for those tasks.
costs
Tradeoffs of using a Dorling cartogram for overview
Sacrifice: Exact region shape and exact adjacency. Risk: Readers may not be able to use the chart for neighbor-finding or shape recognition. Mitigation: If detailed location and adjacency also matter, switch to a contiguous cartogram.
mistakes
Common failure mode for pattern summary
Mistake: Using a rectangular cartogram for a big-picture summary. Why it fails: The severe distortion of shapes and positions makes broad pattern reading less accurate.
check
Check whether the overview is readable
Failure Sign: Readers miss the overall spatial pattern even though the values are present. Quick Check: Ask one summary question on the current cartogram and on a Dorling alternative. Stronger Test: Compare summary accuracy between the current view and a Dorling version on the same broad-pattern questions.
fix
Fix the overview failure
- Replace the rectangular cartogram with a Dorling cartogram.
- Use circles sized by the regional value to simplify the overall pattern.
- If the chart must also support detailed geographic lookup, switch to a contiguous cartogram instead.