A scatterplot is an essential visualization type for understanding the relationship between two measures. Consider a scatterplot when you find yourself asking questions like the following:

• Does how much I spend on marketing really make a difference on sales?
• How much does power consumption go up with each degree of heating/cooling?
• Is there any correlation between hours of study and test performance?

Each of these questions seeks to understand the correlation (if any) between two measures. Scatterplots are great for seeing these relationships and also in locating outliers.

Consider the following scatterplot, which looks for a relationship between the average minutes to service and the average number of days spent in the hospital, broken down by department type and doctor:

The dimensions of Department Type and Doctor on the Marks card define the view level of detail. Color has been used to make it easy to see the department type where each doctor practices. Each mark in the view represents the average minutes to service and average days in the hospital for patients seen by a doctor in a department type. The Size of each circle indicates the total number of patients seen by that doctor.

There does not appear to be much correlation between minutes to service and days in the hospital per doctor. However, the scatterplot is useful for seeing some grouping patterns for doctors within certain departments and also illustrates that Intensive Care (the marks in the upper right) are potentially outliers.