SQL, data modeling, data quality, EDA, visualization · insight-0070
Replace a spaghetti line chart with small multiples that share the same axes
- Evidence type
- practitioner heuristic
- Difficulty
- easy
- Roles
- Data analyst, Data scientist
- Industries
- aviation, retail, energy
Summary: situation, action, reason, boundary
Situation
A chart shows weekly bookings for twelve routes as twelve overlapping coloured lines.
Action
Draw one small panel per route with identical x and y scales, order panels meaningfully (by market or by volume), and highlight the reference series in grey in each panel. Use free scales only when shape matters more than level, and say so in the caption.
Reason
Repeating the same design across panels lets the eye compare shapes; shared scales keep levels comparable and prevent misreading.
Boundary
Many time series, segment comparisons and distribution comparisons.
Symptom or risk
Readers cannot follow any single route, colour legends overload memory, and the one route with an unusual pattern is invisible.
Exceptions
Two or three series that must be compared point by point are clearer on one chart.
Trade-offs
Small multiples need space and lose fine detail per panel.
Pitfalls
Letting the plotting library default to free y-axes, which makes every route look equally volatile.
Lessons and concepts
Claims and their sources
Multi-panel figures (small multiples, also called trellis plots or faceting) should use the same axis ranges across panels and arrange panels in a meaningful, logical order.