The city of Cassadega. (Jon Roberts) Official World Map for George R.R. Martin's series A Song of Ice and Fire, from Westeros to Asshai, from the summer isles to the blasted waste of old Valyria. (© George R.R. Martin, 2012, courtesy of Jon Roberts) This map depicts the frozen lands in the north of Midgard, published in Frozen Empires by Open Design. This was the first region to be illustrated after the launch of the Midgard campaign setting, and was an opportunity for a change in the style of the Midgard maps. (Jon Roberts) Entering the Glacier, an outdoor battle map. (Jon Roberts) An indoor battle map. (Jon Roberts)

In the Northlands of Midgard, the Lung of the Sea blows thick clouds across the Bleak Expanse. In cold years, they reach all the way through the Ironwood Forest to ice the mountainsides of Jotunheim. In another universe, deep in the Milky Way galaxy, humankind has left Earth and settled a planet called Nova Prime. And in the ragged geography of Westeros, a war rages from Castle Black to the Dornish Marches. These are well-known worlds to fans of fantasy and science fiction. However, few know them better than Jonathan Roberts, cartographer of the imagination.

Roberts grew up playing Dungeons & Dragons with his brothers on the west coast of Scotland. “Some of my earliest memories were having my hobbit thief killed by a bunch of berzerkers,” he says. Early on, he took an interest in mapping the imaginary worlds they explored. He kept at his childhood hobby through college and into adulthood, eventually starting his own business, called Fantastic Maps. His is a small, passionate field, and he has risen to the top tier. Last year he feathered his cap by producing the official maps for Game of Thrones. On his site, not only does he showcase his beautiful maps, he offers great tips for aspiring mappers.

“The first thing I do when I get a commission is see if it makes sense,” he says. Realism is important, and even imaginary worlds need to have geographic logic; No sense unduly challenging a reader's suspension of disbelief. This means rivers need to converge as they flow to a coast, mountains form in clusters or lines, and deserts that transition gently into forests. “If you can give people things that make sense to them, then they’ll buy into the world,” says Roberts.

Even though fantasy maps are heavily stylized, it's important to pare them down to the bare essentials, and a working knowledge of real-world geography can help, says Roberts. When he was a boy, he became well-acquainted with the Ordnance Survey, the national mapping authority of Great Britain, while hiking with his brothers in the Scottish countryside. Ordnance maps are busy with topographic contours, trails, rivers, towns, and a plethora of minor map features. But, they economize space logically, without overcrowding. Whenever Roberts has a problem with using space in one of his fantasy maps, he refers back to the Ordinance Survey.

With his deep Scottish brogue, Roberts sounds like he should be narrating the fantasy in addition to mapping it. He seems destined to have fallen into fantasy. He grew up, and learned to roleplay, in an ancient farmhouse with three-foot walls that is so old it is listed in a medieval land inventory called the Domesday Book. On the hill above the house is a Bronze Age fort. Below, a castle hidden in an overgrown valley.

It’s impossible to say when the first fantasy map was made, but most would agree that the maps for Tolkien’s Middle Earth are the benchmark for the genre. “The Lord of the Rings’ maps have an austere style about them,” says map blogger Jonathan Crowe. They combined classical elements, like compass roses and a stylized borders with mountains, towns, and forests were illustrated in profile. Tolkien's books reinvented fantasy storytelling, and made maps an integral part of any fantasy story.

But, even if they look medieval, fantasy maps have almost nothing in common with medieval maps, and in fact would be pretty useless to people in that time. As tools for conducting trade, gathering resources, or waging war, they generally listed locations linearly, without regard to geographic context. Occasionally they would use Ptolemy's grid of latitude and longitude – something you never see in a fantasy map.

A hand-drawn map from one of Roberts' world-building tutorials shows mountains clustered naturally and rivers joining, not forking as they reach the coast. ( Jon Roberts

Crowe's theory is that modern fantasy maps owe more to children's books than they do medieval cartography. “Think about the maps accompanying The Wind in the Willows or Winnie the Pooh,” he says. He points out that The Hobbit was originally a children's book, with illustrations and maps. “When _The Lord of the Rings_ came along it shed the illustrations – by this point it was an adult book, after all, and illustrations were for children – but kept the maps.”

Fantasy maps need to toe a line between fantastic, imaginary worlds and modern brains that trained by things like GPS and Google Maps to process spatial information in very rational ways. If your mountains are oddly clustered, your rivers fork as they flow to the ocean, or countries' borders aren't clipped to natural barriers, then you'd better have an explanation ready. But, that's the whole point of fantasy, right?

One of Roberts' favorite maps is of the Midgard world, designed by legendary game designers Wolfgang Baur and Jeff Grubb. There, in the middle of a verdant, lush continent reminiscent of central Europe is a blasted desert. When Roberts asked for an explanation, he was told that this was the site of an ancient cataclysm. He grins and his face brightens as he explains, “And there's these old monsters who move on like decades timescales, like one footstep will take a decade! But, the whole place is like a blasted, riven landscape, with canyons through it in the middle of this verdant forest, and it was all because of this magical catastrophe!”