matplotlib-data-visualization

Storytelling with Data: Chart Design Guidelines for Matplotlib

This skill focuses on visualization design principles for creating clear, compelling charts that communicate your data's message. It is not a matplotlib API reference — it is a guide for making charts that are easy to read, honest, and visually appealing.

Choose the Right Chart Type

Avoid pie charts for most use cases. Human perception is poor at comparing angles and areas. Use horizontal bar charts instead — they are the easiest chart type to read for categorical comparisons.

Avoid grouped bar charts. Side-by-side bars are hard to compare across groups. Use stacked bar charts if the message is about part-to-whole composition, or a slope chart if the message is about the change between two groups or time periods.

Use horizontal bar charts for categorical comparisons. They allow natural left-to-right reading and accommodate long category labels without rotation.

import matplotlib.pyplot as plt

categories = ["Customer Support", "Engineering", "Marketing", "Sales", "Operations"]
values = [82, 95, 67, 78, 71]

fig, ax = plt.subplots(figsize=(8, 4))
bars = ax.barh(categories, values, color="#cccccc")
# Highlight the key bar
bars[1].set_color("#e63946")
ax.set_xlim(0, 110)
ax.set_title("Engineering leads in satisfaction scores", loc="left", fontweight="bold")
ax.spines[["top", "right", "bottom"]].set_visible(False)
ax.tick_params(left=False)
ax.xaxis.set_visible(False)

# Label bars directly instead of using an x-axis
for bar, val in zip(bars, values):
    ax.text(bar.get_width() + 1.5, bar.get_y() + bar.get_height() / 2,
            str(val), va="center", fontsize=10)

plt.tight_layout()

Use vertical bar charts when the x-axis represents chronological progression. Time reads naturally left-to-right on a horizontal axis.

Use line charts to show continuous data over time. Lines clearly convey trends, rates of change, and patterns. Use them instead of bar charts when the focus is on the shape of change rather than individual values.