Line graphs show change — Data, 7–10 years
A line graph helps us see how a measured amount changes from one time to the next. Data, 7–10 years.
A line joining measurements
A line graph places measurements at different times and joins them in order. The height of each point shows the amount, while the line helps your eyes follow rises, falls and flat parts. It is especially useful when time is part of the question.
Why connect the points?
A table tells you each measurement, but it can be slow to scan for a pattern. Connecting measurements in time order makes the direction easier to see. The graph was designed to answer questions such as “When did the temperature rise fastest?” rather than just list temperatures.
Reading a temperature graph
A thermometer records 10°C at 8:00, 12°C at 10:00, 15°C at 12:00 and 14°C at 14:00. Plot each time and temperature, then join the points. The line rises by 5°C from 8:00 to noon, then falls by 1°C, so noon was the warmest reading.
The line is not extra data
It is easy to think that every point along a joining line was measured. Usually only the marked points are actual measurements; the line shows the change between them. If readings were taken only at 8:00 and noon, the graph cannot prove what happened at 9:30.
Following change in real life
Line graphs can show rainfall across a week, a plant’s height across several weeks or the number of visitors to a museum each day. They are most honest when the measurements have a natural order, such as time. They are not the best choice for unrelated categories like favourite colours.
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