Near the end of 1861, with the American Union crumbling, President Abraham Lincoln became obsessed with an unusual document. Nearly three feet in length, it appeared at first to be a map of the southern states. But it was covered with finely rendered shading, with the darkness of each county reflecting the number of slaves who lived there. South Carolina, the first to secede from the Union, featured a particularly dark coastline. Yet other parts of the South (like western Virginia) appeared as islands of lightness.

Lincoln often studied the map, and it “bore the marks of much service,” according to a memoir by Francis Bicknell Carpenter, an eminent painter who was at the White House conducting research for a portrait of the President. At one point, Carpenter borrowed Lincoln’s map so that he could include it in the painting. Some time later, the President visited him in his studio and, spotting his precious map, declared, “Ah! … you have appropriated my map, have you? I have been looking all around for it.” Then Lincoln slipped on his glasses, sat on a trunk by a window, and “began to pore over it very earnestly.”

In the map, Lincoln saw testimony that the American south was not a uniform bloc. Areas of heavy slavery—the darkened banks along the Mississippi River, for example—tended to be secessionist, but the areas in between held the hope of pro-Union sympathy. Unlike traditional cartography, the map was designed to portray political terrain and, in Lincoln’s mind, moral terrain. The President called it his “slave map.” Today we would call it an infographic.

Infographics are clearly having a cultural moment. They have become pervasive in newspapers, magazines, blog posts, and viral tweets; they appear on television and in advertising, in political campaigns and at art openings. As a Google search term, “infographic” has increased nearly twenty-fold in the last five years. Yet infographics have been popular, in one form or another, for centuries. The source of their power isn’t computers or the Internet, but the brain’s natural visual intelligence.

Credit for the world’s first infographics should probably go to William Playfair, a Scottish engineer, economist, and failed silversmith. In 1786, Playfair published the “Commercial and Political Atlas,” which included the first known line graphs. In one graph, for example, Playfair showed England’s exports and imports in a single chart: in the seventeen-fifties, the export line shoots up, and around the middle of the decade it crosses the import line, showing a trade surplus. Until that time, economists worked with expanses of figures arranged in rows and columns. With Playfair’s innovation, the numbers became dots connected in space and their broader meaning became immediately apparent.

The importance of what he had done was not recognized at the time, but Playfair, who also invented pie charts and bar graphs, had found a way to take advantage of a potent pattern-recognition machine: the human brain. From the first moment that animals on earth developed sight, the advantage went to those who were fastest to discern the patterns, or unusual details, that signalled potential threats—or potential opportunities. The human brain has been shaped by eons of evolution to make immediate sense of its surroundings. Roughly half of the human brain is involved in processing images. Playfair took information that is not easy for us to absorb (columns of British import-export figures) and put it into a form (a landscape of peaks and valleys) that the brain can interpret with speed. This is the idea behind all infographics.

“They can act as a cognitive prosthetic,” says Stephen M. Kosslyn, a former Harvard scientist known for his work in vision who is now the founding dean of the Minerva Schools at the Keck Graduate Institute.

In the decades after Playfair, Europe came alive with infographic innovation. In 1826, Charles Dupin created a so-called “thematic map” using shading to show the varying levels of illiteracy across France. The German geographer Heinrich Berghaus made this technique famous in the mid-nineteenth century with dozens of works depicting the planet’s climate, animal life, and anthropology. Later in the century, Charles Booth published a map that showed the stunning extent of poverty in London, helping to promote social reforms. Even Florence Nightingale, the mother of modern nursing, invented a new kind of chart to show seasonal changes in casualties during the Crimean War. Called a polar-area chart, it’s still used today.

Since then, technology has allowed maps and infographics to become much more impressive. Even in Lincoln’s time, people could travel across a continent, returning with the data needed for a detailed slave map. But new inventions are also what deepens the hunger for infographics. Think of all the information coming into Lincoln’s office: budgets, political intelligence, reports from distant battle fields. Technology made modern nations possible, but all the measuring, accounting, and reporting can easily overwhelm the human mind. Surely what Lincoln found appealing about his slave map was the way it made a bit of sense of the world.

What is so interesting about infographics today—and the reason they’ve become so popular—is the role they play in today’s escalating information arms race. Data has become “big.” There are so many new forms of media (blogs, Tumblr, Twitter, etc.) that just to make a complete list of them would itself be overwhelming. Like Lincoln, we are all looking for a little help.

Gareth Cook is the series editor of Best American Infographics. He is a Pulitzer Prize winning journalist in Jamaica Plain, Massachusetts.

Infographic: Library of Congress.