Use contiguous cartograms instead of rectangular cartograms for region location lookup
For lookup tasks on geospatial cartograms, prefer a contiguous cartogram type on distorted map views to improve fidelity and mitigate region-location lookup errors for readers finding a region on the cartogram.
- purpose:refine
- basis:empirical
- task:retrieve
- chart:map
- data:geospatial
- quality:fidelity:use
- lever:chart-family
- reading-mode:lookup
advice
Choose a locality-preserving cartogram type
Use a contiguous cartogram when readers must find a region on a distorted map. For example, replace a rectangular cartogram with a contiguous cartogram for locate-the-region tasks.
reason
Why contiguous cartograms help location lookup
Keeping the map visually connected helps readers search by approximate geographic position instead of re-learning a schematic layout.
Mechanism: A contiguous cartogram preserves more of the map’s spatial arrangement than a rectangular cartogram, so readers can use relative location cues to find the target region.
Evidence: In the controlled study, contiguous cartograms outperformed rectangular cartograms on the locate task in both accuracy and time, with statistically significant differences (Nusrat et al., 2018; Zeng & Battle, 2023).
context
Use when readers must find a region quickly and correctly
- User Goal: Find a specific region on the cartogram.
- Task: Locate a highlighted region from the source map in the cartogram.
- Data: Geospatial regions with meaningful relative positions.
- Chart Setting: A static cartogram is used for lookup rather than only for broad summary.
- Success Criterion: Lower lookup error and faster completion.
exceptions
Do not use when exact shape recognition is the main task
Break it when: The main task is recognizing a region by its original outline. Why: Non-contiguous cartograms preserve shape better and were more accurate for recognition.
costs
Tradeoffs of using a contiguous cartogram
Sacrifice: Perfect geometric regularity. Risk: Some region shapes still become distorted. Mitigation: If outline recognition matters more than location lookup, switch to a non-contiguous cartogram.
mistakes
Common failure mode for location lookup
Mistake: Using a rectangular cartogram for find-the-region tasks. Why it fails: The schematic rectangles weaken the relative-position cues that readers use to search the map.
check
Check whether location lookup is working
Failure Sign: Readers take longer or make more mistakes when finding a target region. Quick Check: Run one locate-the-region question on the current view and on a contiguous alternative. Stronger Test: Compare error and completion time for a small set of location questions across the two cartogram types.
fix
Fix the location-lookup failure
- Replace the rectangular cartogram with a contiguous cartogram.
- Keep the cartogram connected so readers can use relative position cues.
- If the task changes from location lookup to shape recognition, switch to a non-contiguous cartogram instead.