Summarize distributions with box plots

Box plots are a staple chart for showing the median, quartiles, and outliers with a single glyph. Comparing categories makes differences in dispersion immediately visible.

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import seaborn as sns
import matplotlib.pyplot as plt

mpg = sns.load_dataset("mpg").dropna(subset=["mpg", "origin"])

fig, ax = plt.subplots(figsize=(6, 4))
sns.boxplot(data=mpg, x="origin", y="mpg", palette="Set2", ax=ax)

ax.set_xlabel("Production region")
ax.set_ylabel("Fuel economy (MPG)")
ax.set_title("Fuel economy by region (box plot)")
ax.grid(axis="y", alpha=0.3)

fig.tight_layout()

plt.show()

Reading tips #

• The box represents the interquartile range (IQR) and the line in the middle is the median. Whiskers typically extend to 1.5×IQR.
• When there are too many outliers, inspect them with another chart or relax the upper bound.
• Flipping the plot horizontally keeps long labels readable.