Line Graphs

Example: Bacterial Growth Curve

  %%{init: {'theme': 'neutral'}}%%
xychart-beta
    title "Bacterial Population Growth Over Time"
    x-axis [0h, 2h, 4h, 6h, 8h, 10h, 12h, 14h]
    y-axis "Population (millions)" 0 --> 500
    line [10, 12, 25, 80, 250, 420, 480, 490]

accTitle: Bacterial Growth Curve
accDescr: A line graph showing bacterial population growth over 14 hours. The population starts at 10 million, remains relatively flat during lag phase (0-4h), enters exponential growth (4-10h) rising steeply to 420 million, then levels off in stationary phase approaching 490 million by 14 hours.

Guidelines for Describing Line Graphs

Create a table

Line graphs can be converted into accessible data tables. Especially if the values are necessary for participation or assessment.

Provide the labels, titles and an overview

Describe visual attributes, and summarize trends

Is the line increasing, decreasing, or showing a pattern? Are there distinct phases?

Note key points

Identify starting values, ending values, peaks, valleys, and inflection points.

You don’t need to describe line styles (dashed, solid) unless they distinguish between different data series that students must differentiate.

Alternative Format Options

Text description captures the story the graph tells.

This line graph shows bacterial population growth over a 14-hour period. The population begins at 10 million cells and shows three distinct phases: a lag phase (0-4 hours) with minimal growth, an exponential phase (4-10 hours) with rapid increase to 420 million, and a stationary phase (10-14 hours) where growth levels off near 490 million.

Data tables provide exact values for analysis.

Time (hours)	Population (millions)
0	10
2	12
4	25
6	80
8	250
10	420
12	480
14	490

Lists work for highlighting key data points.

0 hours: 10 million (initial population)
4 hours: 25 million (end of lag phase)
8 hours: 250 million (exponential growth)
10 hours: 420 million (approaching maximum)
14 hours: 490 million (stationary phase)

Common Mistakes to Avoid

Describing every data point — Focus on the trend and key values, not every coordinate, if data is necessary its best in a table.
Ignoring the shape — “Increases over time” misses important patterns like exponential growth or plateaus
Omitting context — Explain why the pattern matters (e.g., “indicating resource depletion”)

For graphs with multiple lines, describe each line separately and then compare them. Clearly identify which line represents which variable.

Where to Place the Description

Give the description a heading and reference it in the alt text, or otherwise make sure the relationship between the description and image is clear. If the description is placed at the end of the document use #heading reference links to move back and forth.

This article is an adaptation of ‘Complex Images for All Learners’ by Supada Amornchat, used under CC BY-NC-SA 4.0.

Illustrations Maps