Part IV Communicating findings 15.2.3. Pie charts Pie charts are generally used to show percentage or proportional data. Generally, the percentage represented by each category is provided next to the corresponding slice of pie. These are a visual way of displaying data that might otherwise be given in a small table. They are useful for displaying data that are classified into nominal or ordinal categories (e.g. reasons why people are unable to access health services or how satisfied people are with the quality of education in their country). Like column and bar charts, pie charts should display data for around eight categories or fewer. More than this makes it difficult for the reader to distinguish between the relative sizes of the different sectors, making the chart difficult to interpret. 15.2.4. Scatter plots Scatter plots are useful to show how different variables interact with and relate to each other. One variable is plotted on the “Y” axis and another on the “X” axis; their intersecting points show the relationship patterns. For example, in investigating the right to education in your country, you might seek to chart the relationship between expenditure on teachers’ wages and student-teacher classroom ratios across municipalities. Chapter 15: Data and design: Communicating through visualization | 149