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Chart Selection

Match the chart to the question.

Decision flow

  1. What is the question? Comparison, trend, distribution, composition, relationship, geographic
  2. How many variables? 1, 2, or many
  3. What data type? Numeric, categorical, time, geographic

Chart types

Name Use When
Bar graph Compare values across categories Discrete categories on X; values on Y
Bar chart (horizontal) Rank data Long category labels; many categories
Line graph Show changes over time Continuous time on X
Area chart Cumulative trend Magnitude + trend
Pie chart Part-of-whole ≤ 4 slices, sums to 100%
Donut chart Part-of-whole Same as pie; better label space
Map (choropleth/symbol) Geographic distribution Region/country/state data
Histogram Distribution of one variable Bin frequency of values
Box plot Distribution + outliers Compare distributions across groups
Heatmap Magnitude across two dimensions Matrix of values
Scatterplot Relationship between two variables Correlation, clusters, outliers
Bubble chart Three variables (x, y, size) Scatter + magnitude
Sankey Flow between stages Funnel, energy, traffic
Treemap Hierarchical part-of-whole Nested categories
Waterfall Sequential additive change Variance breakdown

Choose by question

Question Chart
"How does X compare across categories?" Bar
"How has X changed over time?" Line
"What's the distribution of X?" Histogram, box plot
"How does X break down?" Stacked bar, treemap
"Is X related to Y?" Scatter
"Where is X happening?" Map
"How does X flow through stages?" Funnel, Sankey

Common mistakes

  • Pie charts with > 4 slices → use bar chart
  • Truncated y-axis → exaggerates differences
  • 3D charts → distort perception
  • Too many colors → audience can't parse
  • Dual y-axes → easy to mislead

Color

  • Sequential — single hue, varying lightness (for ordinal/quantitative)
  • Diverging — two hues from neutral (for centered scales: e.g. -100% / +100%)
  • Categorical — distinct hues (for unordered categories)
  • Test for color blindness (ColorBrewer)

References