By a nice coincidence, it occurred to me just yesterday that I could even implement *treemaps* in Excel charts without using VBA. The details are too much for this margin (oh all right, I'm too lazy to have worked them out, okay?) but I think whoever implements square pie charts the way you call for, will have gone half way to acheiving Excel chart-based VBA-free treemaps.

I submitted a chart-based solution; I'll let Chris talk about it.

While working on this, I realized that I find this chart type somewhat misleading the way it's set up. The area is proportional to the value, but the apparent value seems to be much more than the value. This distortion is particularly true for larger values. For example, the first sample pie is 56%, but a quick glance makes me think the value is closer to 75%. A value of 2/3 appears more like 80%. You can quantitatively see that a value is large or small, but it is not easy to guess the percentage by just looking at the chart.

This kind of chart might be more accurately viewed if the values filled the bottom row of squares completely, then started on the second row, etc.

Yes, I was thinking the same thing as Jon - these charts are not good at showing proportions (because the empty area is spread across two rectangular spaces, rather than one), and can really only reflect a single number per chart. I'm not sure that these can communicate anything that an actual numerical representation can't do, just as easily and in the same amount of space. Imaging trying to read the chart above without the text-based representation on the top - quite misleading.

I like Jon's alternative approach a bit better - kind of a 'glass half-full' chart?

I agree that it is difficult to quickly grasp the realtive chart area in such a chart. Particularly the comparison of the one "full" area to the two "empty" areas. It is in fact a bit easier to interpret areas with the "glass half-full" approach.

It is not true, however, that these kinds of charts can only be used to represent a single number. As with pie-charts, color can be used to represent a moderately small number of data points.

I submitted chart and cell based Excel solutions that implement both the traditional and "glass half-full" approaches as well as examples plotting multiple data values.

Yes, you could use colour, but comparisons of two or more numbers on a single chart would be less than ideal, and more difficult than with a standard pie chart. In my opinion, plain old text, or perhaps bar or pie charts for comparisons of percentages are much more communicative than these square charts. I can't think of any application where these are better (not that there isn't one, of course).