In 1726, Filippo Juvarra put the finishing touches on the dome of the Basilica of Superga, an intricately designed church in Turin, Italy. The artist painted the interior roof of the building with a kaleidoscopic pattern that when paired with the dome’s ring of windows creates the effect of ornate, concentric circles. Nearly 300 years later, in the French town of Cessy, engineers finished building the Compact Muon Solenoid, a massive particle detector that, when viewed in cross-section, bears a striking resemblance to Juvarra’s circular basilica dome.
“These things look so similar, and yet they’re separated by 300 years,” says Manuel Lima. “One is all about religion and spirituality and the other is about science.” Lima, a design lead at Google and creator of the website Visual Complexity, was intrigued by the circle’s ubiquity. “I’ve often wondered, why are humans so fascinated with circles in the first place?” he says.
In his new book, Lima attempts to find out. Book Of Circles: Visualizing Spheres of Knowledge (out May 2) is a follow up to Book of Trees, in which Lima cataloged the use of arboreal models in data visualization from the middle ages to current day. Like his first book, Circles is a thorough taxonomy of circular infographics, but it’s also a deep dive into the psychology behind the the shape’s enduring appeal.
Lima began thinking about the book in 2011 after he was asked a confounding question during a presentation he was giving on Visual Complexity. At one point, a woman stood up and asked why so many of the visualizations he was showing tended to be circular. Lima wasn’t sure. “It sort of bothered me that I didn’t have an answer to that question,” he recalls. And so Lima began researching circles, unearthing the shape’s history one example at a time.
He found that some of the earliest examples of circularity, outside of the natural world, can be traced back nearly 40,000 years to when hunter gatherers would carve spirals and concentric circles onto rocks as a form of communication. Over the years, the circle was adopted as a common motif in architecture, agriculture, city planning, science, and data visualization. As Lima gathered more examples of circularity, he realized the shape wasn’t ubiquitous by simple chance. “There are evolutionary explanations,” he says.
From a psychological perspective, the circle represents happiness, unity, perfection, and wholeness. “It’s a survival instinct,” he says, referencing scientific studies that show how sharp objects activate the amygdala, the part of the brain that processes fear. Soft round shapes, by contrast, appear safer. “A preference for circular shapes is deeply ingrained in all of us from birth,” he writes. “At five months of age, before they utter a word or scribble a drawing, infants already show a clear visual preference for contoured lines over straight ones.”
Our attraction to circularity might be evolutionary to an extent, but Lima acknowledges that the shape is also just really practical. Wheels are round because the shape allows for efficient rotation. The first planetary maps were circular because planets are spheres. Circles, Lima adds, are the simplest geometric shape to draw. “There are no corners, no edges,” he says.
Lima’s historical and psychological research provides the backbone for the rest of his book, which provides a more direct answer to his original question: Why are circles so common in data visualization? Judging by the sheer number of infographics in the book, the short answer is that circles are exceptionally versatile. Lima deconstructs seven main circular data-viz archetypes—rings and spirals, wheels and pies, grids and graticules, nodes and links, ebbs and flows, and so on— and showcases through examples how each is used to arrange information. The book smartly juxtaposes old and new explain how this visual metaphor has at one evolved and remained the same over thousands of years.
In one compelling example, Lima places a circular node from 2012 next to an illustration of a compass from 1549. Cristian Ilies Vasile’s computerized visualization, which visualizes the digits of Pi, mirrors the hand-drawn image on the opposite page. Both are a tangle of lines that intersect to form a web of information. That historical mirroring is intentional, Lima says. “All of these [infographics] are based on or emulated from instances that have happened in the past,” he says. “In many ways that’s what the book is trying to prove.” In other words, circles might not be new, but they sure are effective.