d) Scatter plot and Bubble chart
A scatter plot shows the values of two variables along two axes. The pattern between the points visualises the correlation between them. One of the advantages of a scatter plot is that it can contain way more elements than the chart types mentioned above.
A scatter plot is excellent for emphasising correlations between dimensions. Conclusions are thus highly drawn from the grouping (or the lack of groupings) of the points rather than from the individual points.
For scatter plots it is, however, important to remember that it takes a certain amount of points to make sense. This also goes the other way around – the more points included, the longer it takes to check the visualisation before it can be interpreted. Therefore, if the goal is to achieve a quick insight, the scatter plot may not be the right choice.
The bubble chart is very similar to a scatter plot, but it is characterised in that it allows showing the variation between three data items. The size of the individual bubbles represents the third variable. The chart is quite complex and may not decode fast, but it opens up to other analytic possibilities.