Bar charts on a curve

[Shawna Richter-Ryerson]

I've noticed a lot of papers doing infographic centerpieces with "bar charts" placed on a curve. How does one build such a graph without distorting the data? An information would be appreciated!

[Sajeev Kumarapuram]

Hi, I'm not an expert, but how I do it is... place the bar chart in Illustrator and use the Effect>Warp>Arc.

[Nigel Hawtin]

Best way, and to keep it accurate is to work it out it manually

[Bob Voros]

You can convert percentages, or any value, into degrees of an arc. For example, if you "barc" chart  - I'm copyrighting that - is a semi circle that would be 180• (degrees). So if 100% = 180• then each percentage point would equal 1.8• and all you would have to do is the math on every value - 40% would be 72•, 60% would be 108•, etc.

[martin gee]

i did a blog entry about this on my old website / blog. i'm reposting it here:

a circle walks into a bar chart

Thursday, January 27, 2011

I love the current enthusiasm with infographics and data visualization. I’m hooked. On a regular basis, we see beautiful examples but that’s it. They’re just pretty. Specifically, I’ve been fascinated with circular bar charts (and their Tron-esque aesthetic) but don’t know what I’m looking at most of the time. Due to their nature, they lack a major component: accuracy. 

You can't simply build a circular bar chart from a pie chart (I did use pie charts to make my examples. See fig. b.). With each concentric circle, there’s a different circumference. That’s why runners start at different points to compensate to run the same distance and end at the finish line. On a record, the outer grooves travel faster and farther than the inner grooves. There’s math and geometry behind the “inside track”.

fig. a

Are these all equal? Nope. Each line is 25% of the circle but as a bar chart, each curve's length or value (25% of that circle's circumference) is different. Values below.

fig. b

These 4 curves have the same value / length calculated as a percentage of the circumferences. The same values look distorted. The math is below.

fig. c

Even with a bigger circle and same line weights, there’s distortion at every size.

How can you compare and contrast information if equal values look different?

the math:

First circle: d = 1”, C1 = π • 1” = 3.14“

Red line length = 3.14” x 0.25 = 0.785” = the value I want to show in each line

Second circle: d = 1.25”, C2 = π  • 1.25” = 3.925”

Green line length = 0.785” / 3.925” = 20% of the circumference

Curve drawn from 20% pie chart 

Third circle: d = 1.5“, C3 = π  • 1.5” = 4.71”

Cyan line length = 0.785“ / 4.71” = 16.667% of the circumference

Fourth circle: d = 1.75“, C4 = π  • 1.75” = 5.495”

Orange line length = 0.785 / 5.495 = 14.286% of the circumference

The lengths in fig. a: 0.785”, 0.981”, 1.178” and 1.374”

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These are cool and beautiful ways to show data but are they easy to read and useful? Not really. The battle between form and function rages on and remember to check your math.

[neerajtiwari]

can it be done in coreldraw