All maps courtesy of Uncharted Atlas.

So you want to build a world? Here’s the recipe, at its most basic: Take some topography, then add water.

That was Martin O’Leary’s approach when he decided to build a program to spit out imaginary landscapes. “Essentially, I generate a random bumpy surface so the program has something to start with,” he says. “And then I run an erosion simulation over that.”

Some of the results of that combination—just a small sample of potentially infinite possibility—make up the worlds of the Uncharted Atlas, a Twitter bot O’Leary made to produce a new map every hour, each with its own array of mountains and rivers, fjords, island archipelagoes, and deserts.

The landscapes are rendered in the pen-and-ink style of maps printed at the front of certain fantasy novels à la Tolkien, complete with alien names: “The Pez-mes-Lüch Coast,” “The Confederation of nos-Us,” “Outer Háukwuénoé.” (O’Leary built a language generator, too). But the plain style covers the true-to-life intricacy of the maps. O’Leary—a glaciologist by day—wanted his world-building program to mimic the way landscapes evolve as a result of forces acting over time: Mountains around a river valley, the wide plains sloping to an undulating coastline, thimble islands scattered across the water.

There are less involved ways of generating landscapes, of course. These typically make use of something called “fractal noise”—basically, a pattern of disorder that tends to occur in natural forms, from the complex wending of a river to the craggy silhouette of a mountain. And while it’s a quick way to counterfeit real landscapes, fractal disorder on its own cannot touch the deeper order that organizes a landscape.

“What tends to happen,” O’Leary says of that approach, ”is you get something which looks very good at the small scale, and then there’s no large-scale structure to it.” Picture a river valley, with nowhere for the river to go when it reaches the end.

Uncharted Atlas churns through its meticulous calculations—each map takes about 90 seconds of processing, O’Leary estimates, which is not nothing for modern computing—every hour, and its rivers always reach the sea. “They’re not 100 percent geologically accurate,” says O’Leary. “I would like to go back to it and play with some other stuff. You could do glacial stuff properly, get some proper coastal stuff—I didn’t really do any coastal erosion.”

O’Leary has a habit of turning his “what if” ideas into internet art. Other examples include Botston, an algorithm that fills in new verses for Gaston’s song in Beauty and the Beast (you know the one, and if you don’t, don’t look it up unless you’re prepared to have it stuck in your head for days), and a scale-model of the entire continent of Antarctica in Minecraft. But perhaps the project that shares the most DNA with Uncharted Atlas is called Landsat Bot, which randomly selects a square of satellite imagery every hour and tweets it in all its full-color, painstaking detail. From above, the landscapes can seem just as fantastical as O’Leary’s invented ones, bound together by an astronaut’s-eye perspective.

“I think it becomes hard for us to conceive of how landscapes were thought of before. We’re used to seeing everything laid out on a map with incredible precision,” says O’Leary. Thanks to satellites, “we just take it for granted that you can look at everywhere at once.”