Unit 01.00: The question a chart is answering

A chart that answers no particular question is a table with decoration on it.

One chart, one question

Before choosing a chart type, write the question above the chart. If you cannot, you are still exploring - which is a legitimate activity with different rules.

The code sorts four charts by the question each answers.

CHARTS = [
    ("monthly revenue, 24 months",
     "is revenue growing?", "yes -- a trend question"),
    ("revenue by region, one month",
     "which region is largest?", "yes -- a comparison question"),
    ("everything we measured, on one axis",
     "?", "NO -- no single question"),
    ("one number, very large, in the middle",
     "what is the figure?", "yes -- but a sentence would do"),
]
print(f"{'chart':38} {'question it answers':30} earns its space?")
for chart, question, verdict in CHARTS:
    print(f"{chart:38} {question:30} {verdict}")

print("\nA chart that answers no single question is a table with decoration.")
print("A chart that answers a question a sentence could answer is a sentence.")

# Write the question above the chart before drawing it. If you cannot, you are
# not ready to choose a chart type -- you are still exploring, which is a
# different activity with different rules.

The third row has no question at all, which is what "everything we measured on one axis" produces. The fourth has one, and a sentence would have answered it - a single figure with no comparison does not need a chart.

Exploration charts are different: many questions, quickly, for your own eyes. They should not be the ones you ship.

The mistake this prevents

The mistake is choosing the chart type first. Bar or line is a decision that follows from the comparison, and the comparison follows from the question - so picking the type first means the question gets reverse-engineered to fit it.

Takeaway

Write the question above the chart before drawing it. A chart answering no single question is a table; one answering a question a sentence could answer is a sentence.

Mark complete