Sean C. asked a question that has been on my mind for some time: what do we think of treemaps? Are they too busy? Do they add to our understanding of the data?
Generally, this type of chart is pretty good for exploration but not so for communication. We can stare at the chart however long and still it isn't clear what the designer wanted to convey.
Sean used it to show the components of Australia's CPI and to explain the source of recent inflation.
It does present the hierarchical structure of the data in a compact way. It also provides information on both the relative importance of each factor, together with its growth rate, with little fuss.
That said, the differing sizes and orientations of the boxes makes it hard to compare their sizes. For example, is "home purchase" on the lower left larger than "financial services" in the middle? How about household services (blue on the top) relative to audio, visual and computing (blue on the lower right)?
Also note that the two data series do not carry equal weight: readers are likely drawn more by the box sizes than by color gradations (which do not convey relative values well); as a result, the composition of the CPI rather than the changes in the components will gain more attention.
If the purpose of the chart is to communicate findings, then a data table enhanced with colors and boxes can do a good job. There are other ways to utilize the tabular format, such as sparklines or other symbols in lieu of numbers.
That said, the treemap is more intriguing and inviting than a table of numbers.