When PJ Mode began to purchase old maps in the 1980s, he set out to amass a typical collection of world maps. But along the way, his attention turned to unusual maps that dealers weren’t sure how to categorize—those that attempted to persuade rather than convey geographic information.

“Most collectors looked down their noses at these maps because they didn’t technically consider them maps,” Mode says. “But they were fun and they were inexpensive, and over the years I became more interested in them than the old world maps.”

The interest has culminated in a collection of more than 800 “persuasive maps,” as they are now called, which can be found in digital form through Cornell University’s library. Mode has sorted them into themes, from imperialism to religion to slavery, many with meticulous notes about their history and meaning. One of the oldest, from a 1506 Italian manuscript, gives an overview of hell, while more recent acquisitions include a facetious 2012 New Yorker cover of the Second Avenue subway line.

Marc-William Palen, a University of Exeter history professor and author of The “Conspiracy” of Free Trade, recently came across the collection. “I got lost in it for days,” he says. Palen, who specializes in British and American imperialism, was particularly taken with an 1888 map depicting the trade policy platforms of the year’s presidential candidates, Democratic incumbent Grover Cleveland and Republican Benjamin Harrison. While Cleveland and his party supported free trade, the Republicans’ platform was deeply protectionist.

The map, titled “The Whole Story in a Nutshell!”, shows a jowly Cleveland below a slim Harrison, who is placed among soothing pastel-colored states, while a number of states surrounding Cleveland are a foreboding gray. The map declares that Harrison (the eventual victor) will “protect American labor” and products such as lumber, iron, rice, corn, hemp, and fruits, while Cleveland will destroy wool growers, miners, and the like. Near Cleveland, in the bottom left corner of the map, is the seal of the Cobden Club, a London-based group that supported free trade. This, Palen says, shows how phobias around free trade at the time were focused on Britain.

Such a map is clearly persuasive. But don’t all maps persuade in some way? The oft-used Mercator projection, after all, is only one way of depicting the world. And how does Mode draw the line between persuasive and “factual?”

“I wrestle with this a lot,” Mode says. “Every map is somewhere on a spectrum between objective and subjective.” Perhaps the most plainly persuasive maps in the collection are promotional ones—those that aim to sell something or highlight a business—such as one of Greater New York City published in the late nineteenth century by the horse company Fiss, Doerr, and Carroll.

The outfit, which proclaimed itself the “largest dealers of horses in the world,” occupied an entire block of Manhattan and in 1897 sold an average of 900 horses weekly. The map gives a bird’s eye view of the city—a technique Mode says was popular at the time—and thus sends a message about the company’s scope of operations. It was intended to be posted in elevated stations throughout New York. “They were a huge company,” says Mode, “and this was the peak of their power. Ten years later, they were selling vehicles, and 20 years later, they were out of business.”

Other maps may only reveal themselves to be persuasive after careful scrutiny. Mode points to one of the British empire from 1890. A quick look shows nothing out of the ordinary: Britain’s colonies are shaded in pink. But on closer inspection, the viewer might notice that the map displays 490 degrees of longitude rather than 360 degrees—allowing it to show India, Australia, New Zealand, and other colonies twice, making the empire appear even larger than it already was.  

“Though this is a close call, it fits my collection,” Mode says. “There’s no other reason to show those countries twice.”

People generally take maps at face value. Mark Monmonier, in his book How to Lie With Maps, points out that while American students are often taught to analyze words—to be “cautious consumers” of them—they are seldom taught to do the same with maps. Persuasive cartography reveals how maps manipulate and should be regarded with a critical eye, a lesson that’s perhaps even more important in the present political climate.

As Mode recently wrote in The Portolan, the journal of the Washington Map Society, “[I]n these times of ‘alternative facts,’ we all benefit from a world in which the motives and interests and techniques behind all maps are rightly subject to more rigorous—and more skeptical—analysis.”