Zero Baselines.
Bars and areas start at zero. Lines are exempt.
Bar charts and area charts must start at zero. Without a zero baseline, a 2% change can look like a 200% change. Line charts are exempt because they encode rate of change via slope, not magnitude via area.
Stephen Few, 2012 · Show Me the Numbers
Charts that apply this principle
Bar Chart
Compare quantities across categories using vertical bars positioned on a common baseline.
Diverging Bar Chart
Bars extend left and right from a central baseline to show positive and negative values.
Horizontal Bar Chart
Bars drawn horizontally, ideal when category labels are long or numerous.
Pictogram Chart
Uses repeated icons to represent quantities. Engaging but imprecise.
Polar Area Chart
Smooth continuous area plotted in polar coordinates. Ideal for cyclic data (24-hour cycles, compass directions, monthly seasonality).
Stacked Area Chart
Layered areas showing how parts of a whole change over time.
Stacked Bar Chart
Bars divided into colored segments showing composition per category.
Density Plot
Smooth continuous estimate of a distribution using kernel density estimation.
Error Bar Chart
Bars annotated with ± error markers — the scientific publication standard for mean ± SD or 95% CI comparisons.
Histogram
Shows frequency distribution of a numeric variable by grouping values into bins.
Q-Q Plot
Compares a distribution against a theoretical distribution (e.g. normal) point by point.
2D Contour Plot
Contour lines showing density of points in 2D space, like a topographic map.