Place choropleth maps side by side when comparing multiple parties
For comparing multiple groups across the same districts, use a small-multiple layout instead of a single choropleth map to improve insight and mitigate one-map overload for readers scanning regional patterns.
- purpose:select
- basis:heuristic
- task:compare
- structure:small-multiples:use
- structure:single-view:avoid
- chart:choropleth
- data:geospatial
- quality:insight:use
- lever:layout-structure
advice
Split the map into side-by-side panels
Place multiple choropleth maps side by side when you need to show vote shares for more than one party. For example, use a few aligned district maps for several parties instead of forcing one choropleth map to carry all parties’ vote shares at once.
reason
Why side-by-side panels work
Separate panels let each district keep one value per map, while the shared geography across panels makes cross-party patterns visible.
Mechanism: One district can only encode one party’s vote share in one choropleth at a time, so splitting the view prevents that encoding conflict.
Evidence: The post states that each district in a choropleth map can only show the vote share of one party at a time and recommends placing a few maps next to each other to show multiple parties and reveal patterns (Muth, 2021).
context
Use when one map is not enough
- User Goal: Compare regional patterns for several parties.
- Task: Scan the same districts across multiple vote-share views.
- Data: Multiple district-level vote-share series for the same geography.
- Chart Setting: The maps can be placed next to each other.
- Success Criterion: Readers can compare patterns across parties without losing the district geography.
exceptions
Do not use when only one party is being shown
Break it when: The map needs to show the vote share of only one party. Why: The post says a single choropleth can show one party’s vote share at a time.
costs
Tradeoffs of side-by-side panels
Sacrifice: The layout uses several maps instead of one. Risk: The comparison weakens if the maps are not placed next to each other. Mitigation: Keep the maps adjacent so readers can scan across them.
mistakes
Common failure around side-by-side panels
Mistake: Try to show several parties’ vote shares in one choropleth map. Why it fails: Each district can only show one party’s value at a time.
check
Check whether one map is overloaded
Failure Sign: One choropleth is expected to represent more than one party’s district vote share. Quick Check: Count how many party values each district must show; if it is more than one, compare the single-map attempt with a side-by-side layout. Stronger Test: Verify that each panel reuses the same district geography so the regional patterns can be compared across panels.
fix
Fix the overloaded choropleth
- Split the single map into separate choropleth panels.
- Place the panels next to each other.
- Keep the same district geography across all panels.