Line graphs

Key points

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A line graph is used to spot trends in data over time.

A line graph is a type of graph used to spot in data over time, eg hours in a day or months in a year. The data points are joined together by .
In a line chart the is usually represented on the scale. The labelling on the scale represents the increments of time.
Some line graphs use a false origin. A false origin allows the vertical scale to start at a different value.

How to create a line graph

In order to produce a line graph, data is required. The data often comes in the form of a table.
To create a line graph:

Look for the largest frequency in your table.
Draw a on your square paper or graph paper.
Choose an appropriate scale for this axis and label your axis up to the largest frequency.
Look at how many subdivisions are needed for the .
Draw and label the horizontal axis.
Plot each data point, based on the frequencies and time intervals.
Join each data point to the next, using straight lines.
Check you have labelled each axis correctly, and give your line graph a title.

Examples

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A student recorded how much time they spent reading during a week. The table shows the results. Construct a line graph to represent the data.
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First, identify the largest frequency. The largest frequency is 8. The vertical scale must go up to at least 8
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Draw the vertical scale and number it in regular intervals. In this example, the scale is increasing in increments of one hour. The label for the vertical axis is the frequency, or in this example, the number of hours.
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The horizontal axis needs to be labelled with the unit of time. In this example, the scale is days of the week. Unlike a bar chart, the labels go on the lines, not in the spaces.
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Draw each data point in the correct place and mark it with a cross. For example, Monday is 4 hours. The cross should be vertically above Monday and horizontally in line with the 4 on the vertical axis.
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Finally, join the data points with straight lines and give the graph an appropriate title.
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It is also possible to read data points and make comparisons using a line graph. This line graph represents the average temperature during a year in Greece.
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Using the vertical scale, the temperature of each data point can be read. The scale is going up in increments of 10. Between each multiple of 10 is ten subdivisions. Each subdivision is worth 1°C. The average temperature in May is 21°C.
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By finding the difference between the highest and lowest temperatures the range can be found. The hottest month is August with an average temperature of 32°C. The coldest month is February with an average temperature of 10°C. Range = 32 – 10 = 22. The range is 22°C.
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This line graph shows the electricity production in the UK each quarter. A false origin has been used on the vertical scale, allowing it to start at a different value. The scale is going up in increments of 10. Between each multiple of 10 is ten subdivisions. Each subdivision is worth 1 TWh (Terawatt hour). The least energy, 68 TWh, was produced in the third quarter.