Which visualization technique shows relational data among clusters?

The choice of the circle pack as the visualization technique that shows relational data among clusters is correct due to its ability to effectively represent hierarchical relationships in data. In a circle pack, data points are represented as circles where the size and position of each circle can indicate different relationships and metrics within the data set.

This technique is particularly useful for visualizing clusters, as it allows the user to see how data points are grouped or connected. By arranging circles in clusters, one can quickly understand the relationships between different categories or groups and how they relate to each other in terms of size or quantity.

Other visualization techniques like line charts, bar graphs, and pie charts typically focus on showing individual data points or comparisons between categorical data but do not inherently convey the concept of relational clustering in the same way that circle packs do. While line charts visualize trends over time, bar graphs compare quantities, and pie charts show parts of a whole, none offer the same clarity in representing clusters and their interrelationships as the circle pack visualization does.