In a tree map, what does the size of the blocks represent?

In a tree map, the size of the blocks is representative of values of the measured data. This visualization technique is specifically designed to convey quantitative information through the area of each block, thereby allowing users to easily identify and compare different values at a glance. Each block's area correlates directly to the measure being represented, enabling an immediate understanding of the relative sizes of the various categories or segments.

While there are other aspects to a tree map, such as the arrangement of blocks that can indicate hierarchical relationships (leading towards nominal categories) or how they might reflect percentages of the whole, it is the actual size corresponding to the measured data that is a defining characteristic of this visualization tool. This makes it particularly useful in scenarios where users need to assess part-to-whole relationships and quantitative sizes simultaneously.