24.5 Time series and line graphs — Learn
Prerequisites: coordinates, scales and reading points from a graph.
Objectives: read and construct a time-series table and line graph; describe changes over time.
A time series is data collected at different times. Put time on the horizontal axis and the measured quantity on the vertical axis. Choose an even scale, label both axes with units, plot each point, then join points in time order.
Example. Rainfall was 4 mm in January, 7 mm in February and 5 mm in March. Describe the change.
From January to February it rises by mm.
From February to March it falls by mm.
The line graph shows a rise followed by a fall.
When a scale does not begin at zero, show a clear break. The line graph still shows change over time, but the vertical scale affects how steep the changes look.
Watch out. Do not join points in a different order. The horizontal positions represent time, so keep the dates in sequence.
Progress check
Return to the travel survey. How could monthly counts show whether travel choices changed during a year?
You should now be able to
- organise time-series data in a table;
- construct and read a line graph with labelled axes and a suitable scale;
- describe rises, falls and unchanged values over time.