Charting : Axis, Labels and Legends

Labels

Once a chart has been created it is important that appropriate labels are added to it so that it is clear what the chart shows. All charts need a title to state what the purpose of the chart is.

If a chart has axis then each axis should have also a label. The axis running along the bottom of the chart is the X axis and the axis running up the side of the chart is the Y axis. An axis label should clearly state what the axis measures and what units have been used on the scale.

Axis Scales

When you draw a chart by hand you need to decide what range the axis will cover, i.e. what will be the lowest value you will plot on the axis and what will be the highest value. You also need to decide how you will divide the axis up, i.e. into steps of 5, 10, 50 etc. This axis has a range of 100 to 200 and goes up in steps of 50 :

If you use a charting package to produce a chart then it will automatically set the axis ranges and steps for you by looking at the data you have entered. However in some circumstances you may want to adjust these manually. Most charting packages will let you do this. You need to be careful that when you adjust the axis ranges you do not move any data points off the chart.

Legends

Sometimes you may want to show more than one set of data on the same chart. For example :

• You may want to show the temperature in each month of two different years to show that one year had a warmer summer than the other.
• You may want to show how the time it takes for a liquid to cool is different when the liquid is placed in two different shaped containers.

If this is the case then both sets of data are plotted on the same chart using different colours or patterns to distinguish them. A legend or key is then added to identify the two sets of data.

GCSE ICT Companion 04 - (C) P Meakin 2004