Pie charts

Use these to show the different proportions of parts of a whole. Work the proportions as follows:
1	If your data are in raw figures, calculate the percentage of the whole for each category.
2	Translate this percentage into a sector of a circle by multiplying the percentage by 3.6 (i.e. 360 degrees divided by 100).
3	Decide on the size of the circle to use and where to start with the first category.
4	Draw in the sectors using a protractor to measure the angles between the sectors.

Guidelines

• Use a small number of categories. If you have more than six, try to combine categories.
• Label categories directly and add percentages. Avoid using a key if possible.
• For comparison pie charts:
  • where the totals of the pie charts differ, draw them so that their areas give some indication of these differences
  • keep equivalent segments in a similar place (in other words, work consistently around each pie either clockwise or anticlockwise, starting with the same category in the same place)
  • if there are more than three pie charts to compare, think about using stacked bar charts instead.

Guidelines for bar charts

• Use vertical or horizontal bars; horizontal bars look better with long labels.
• Label both axes, but keep labels outside the bars so they don't obscure the sizes.
• Keep unconnected bars separate from each other.
• Put bars in a logical order (e.g. arranged by age or date or length of bar).
• Don't have more than two or three bars in a grouped set unless absolutely necessary.
• Use stacked bar charts rather than pie charts for comparing more than three sets of data.
• The components of a stacked bar chart should show their percentage of the whole.

Guidelines for line graphs

• Don't put too much information on one graph. How many curves you can include will depend on how close they are to each other and whether they intersect.
• Start the vertical axis at zero unless you have a good reason not to. In this case, draw attention to what you have done.
• Label the axes and curves clearly. Include the units (e.g. thousands or percentages) as well as the variable names.
• Make clear distinction between curves on the same axes. Distinguish between them with different types of line (solid, dotted, etc.) and by using colour where possible. Avoid using keys.
• For time-series graphs: if you are using totals, plot them at the end of the period to which they relate; if you're using averages, plot them at the midpoints.
• If the graph is to be used to extract values, the curve lines will have to be quite thin so that this can be done accurately.