If the trailers for the upcoming fourth season of Game of Thrones are to be believed, HBO’s famously expansive fantasy series will soon be heading to all-new locations, including the lagoon city of Braavos and the towering pyramid of the slave city Meereen. There’s a depth and detail to the world of creator George R. R. Martin that has still only been partially revealed by the books and the show; but for those who yearn to know more about the worlds of Westeros and Essos, the detailed and often mysterious official maps for the series may hold clues not only for where the show is heading, but what lies in the dark lands at the edge of the known world where not even the books have dared to tread.

Rather than scientifically precise cartography, the maps are intended to represent what Westerosi Maesters — scholars and learned men — would have been able to create. That’s why the maps contain no scale or compass, and much like the early world maps of the past, why they should not be considered perfectly accurate for calculating relative distances. Still, Roberts told WIRED, there is a a rule of thumb that says the Wall is 300 miles long, “so you can use that to get a sense of scale for the world, making Westeros a few thousand miles long. Westeros is pretty huge.”

When he first began work on the project, Roberts received scans of all George R. R. Martin’s paper maps and started stitching them together in Photoshop to create a master map for the rest of his work. Thanks to Martin’s legendary attention to detail, however, it was a far easier process than anticipated.

“Normally, for a big project, I expect inconsistencies between maps and there’s always a stage of cleaning up these edge cases,” said Roberts. “This was the exception — those pencil maps lined up perfectly. It made my life amazingly easy. George provided keyed notes to all the major areas, particularly the new regions.” Martin’s notes also included real-world locations to be used for visual reference in different cities, and “some colorful descriptions,” like a note that the island called The Paps had been named for its resemblance to a woman’s chest. “I was kindly asked to make them more representative,” said Roberts.

Some areas of the world, like the medieval metropolis of Kings Landing, already had their own reference maps, while other locations like Braavos had never been sketched out until Roberts envisioned them — with detailed input from Martin, of course. Roberts says he listened to the relevant chapters of audiobooks from the series that were set in Braavos as he traced the routes, so that the map would allow readers to track the movements of certain characters as they move bridge by bridge through the city. Roberts provided WIRED with a series of process shots for the Sealord’s Palace (below), the Braavosi seat of power.

Like many of the most interesting details of the map, Braavos is located in in Essos, the eastern continent that is home to Daenerys Targaryen but largely unexplored by the people of Westeros. Because the map is limited by the knowledge of the Westerosi, that means that details of the east are far more scant and mysterious, including cities, mountains and seas that have never appeared in the books or the show — at least so far. “If you see something in those eastern lands,” says Roberts, “you can be sure it’s there for a reason.”

Several locations appear on the map that have never before been mentioned in the books, including the Cities of the Bloodless Men, the Great Sand Sea, the Grey Waste, the Cannibal Sands, the City of the Winged Men, and the jungle continent of Ulthos, which lies south of the Shadow Lands.

Fans of True Detective may also notice one other surprising location on the easternmost edge of the map: the city of Carcosa. Originally a strange and ancient city mentioned in the Ambrose Bierce Short story “An Inhabitant of Carcosa” and the influential Robert Chambers book The King in Yellow, references to Carcosa and its “Yellow King” have made their way into numerous works, from Stephen King stories to the mythos of H.P Lovecraft to HBO’s recent detective drama — and now, seemingly the world of Game of Thrones as well.

Again, the maps represent not an objective or scientific view of Martin’s world, but rather what Westerosi scholars know about it. “The furthest cities are placed by rumor rather than fact, and the accuracy of the far reaches should be taken with a pinch of salt,” said Roberts. “Not all locations should be taken as rote, and the drop in detail to the east of the Bone Mountains reflects the drop in the amount of information available.” That makes it even more interesting that Carcosa, described by Chambers as a lost city where “shadows lengthen,” resides just north of the Shadow Lands on the southeastern shore of the Hidden Sea, at the outer limit of the world’s knowledge.

Other clues about the lands to the east may lie even in the color of certain map features. The Shadow Lands, for example, are colored a much darker gray because of the enigmatic “Shadow” said to cover it, with interstitial pink shading for the invasive “ghost grass” that the Dothraki believe will one day cover the entire world. “The Shadow Lands are dark to reflect the biases of the Maesters as well as any actual Shadow,” said Roberts, though he adds he is not privy to the details of what causes it. “The pink ghost grass? Well, that’s definitely not natural.”

Two eastern seas that were named for the first time by the maps, the Bleeding Sea and the Sea of Sighs, also appear in distinctive and different shades of pink and red. “These are landlocked seas, and so are quite unusual. I can tell you they’re colored this way for a reason, right down to adjustments to the specific shade,” said Roberts. “It was very clear that getting the details right was going to be important, and with all that has been created and written about Westeros and Essos, that [was] a huge challenge.”

Although Game of Thrones fans have largely been supportive and inquisitive about the maps, Roberts says his favorite response so far came from a reader who bought The Lands of Ice and Fire on Amazon.com thinking it was Winds of Winter, the long-awaited sixth book in the novel series. “He gave the product one star — but decided to keep it because he ‘liked the pictures.’”