Re: Proportional Venn Diagrams

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On Tue, 28 Aug 2007, in microsoft.public.excel.charting,
Nevet <Nevet@xxxxxxxxxxxxxxxxxxxxxxxxx> said:
I'm looking to create a Venn diagram that depicts not only relationships
among entities but also their relative size. For example, Group A is of size
60, Group B, size 30, is a subset of A; Group C, size 20, is also a subset of
A, and includes an overlap of 15 with group B. In other words, B & C are
partially overlapping, and both fully included in A. I would like the
circles' areas and the overlapping portion to be proportionate to their
sizes.

Since you say B and C are entirely inside A, your problem boils down to getting just two circles to overlap. I once used trigonometry in a BASIC program, to work out where two such circles should be, although I don't have the equation to hand anymore. You can get the proportionality of the circles easily enough using a Bubble Chart type, but Excel bubble charts don't preserve the relationship between bubble radius and XY scale properly, so trigonometry wouldn't work there. If you wanted to use Excel for the calculation and graph drawing, you'd have to draw circular lines instead, using XY series.

To be honest, I doubt the value to your audience of meticulously-calculated circles would be worth the effort, especially as you have only one graph to draw. Have you considered just using a drawing program and doing it freehand, estimating the proportions by eye? Or maybe you could use the spread*** to create a rectangular version, setting the cells to squares and coloring them in? This would have the advantage that the readers could count the squares exactly.

--
Del Cotter
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