Interactive Line Charts

When to reach for a line chart

A line chart is the go-to shape for change over an ordered axis — almost always time (days, months, years). The line itself draws attention to trend: is the metric rising, falling, or flat? Markers on top of the line let you also read off exact points without losing the trend shape.

Basic interactive line

Interactive line

import pandas as pd
import plotly.express as px
 
df = pd.DataFrame({
    "date": pd.date_range("2025-01-01", periods=7, freq="D"),
    "orders": [120, 140, 130, 160, 155, 170, 180],
})
 
fig = px.line(df, x="date", y="orders", markers=True, title="Daily orders")
fig.show()

Because this is Plotly (not Matplotlib), the rendered chart already lets you hover each marker for its exact date/value, drag to zoom into a date range, and double-click to reset.

Multiple lines (color)

Multiple lines

import pandas as pd
import plotly.express as px
 
df = pd.DataFrame({
    "date": list(pd.date_range("2025-01-01", periods=5, freq="D")) * 2,
    "orders": [120, 140, 130, 160, 155, 100, 110, 120, 125, 140],
    "product": ["A"] * 5 + ["B"] * 5,
})
 
fig = px.line(df, x="date", y="orders", color="product", markers=True, title="Orders by product")
fig.show()

Passing color="product" does two things at once: it splits the data into one line per group, and it adds a legend you can click to hide/show a series.

sketch A line chart, traced point by point p5.js Pause Restart

The line connects ordered points on an x-axis; the traveling dot mimics hovering along the series.

Tips

• Use hover_data=[...] to show extra fields (e.g. region, channel) in the tooltip.
• Use fig.update_layout(...) for axis labels, margins, and legend position.
• Sort your DataFrame by the x-axis column first — Plotly draws points in row order, so an unsorted date column produces a zig-zag line.

Analyst’s tip

A line chart implies continuity between points — the eye reads the connecting segment as “what probably happened in between.” Only connect points that are genuinely on the same continuous axis (like consecutive days); connecting unrelated categories with a line invents a trend that isn’t there. That’s what bar charts are for.

diagram Choosing a line chart mermaid

  flowchart TD
  A["Is the x-axis ordered
and continuous (time, sequence)?"] -->|"Yes"| B["Does trend/direction
matter most?"]
  A -->|"No, unordered categories"| C["Use a bar chart instead"]
  B -->|"Yes"| D["px.line(...)
add markers=True for exact points"]
  B -->|"No, comparing totals"| C

Line charts fit ordered, continuous axes where trend matters more than exact category comparison.

Next

Continue to: Interactive Bar Charts for comparing categories.

🧪 Try It Yourself

Exercise 1 – Draw a Line Chart

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Exercise 2 – Show the Markers

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Exercise 3 – One Line per Group

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