The Walls were built more than a century ago when humanity was brought to the edge of extinction at the hand of the Titans. In response to this looming threat, the humans made huge walls to protect their last stronghold.
We’re going to explore the outside world someday, right? Far beyond these walls, there’s flaming water, land made of ice, and fields of sand spread wide. It’s the world my parents wanted to go to - Armin Arlert
We know that: 1.) There are English, German, and Scandinavian names in SnK 2.) We have a singular Native American name (Nanaba) when there would likely be more if this was North America 3.) Armin expresses both wonderment and bewilderment at the concept of “Fire Water” - Lava, “Snowfields of Sand” - Deserts, and “Continent[s] of Ice” - Tundra. These are all types of environments that they are unfamiliar with living inside the walls. This means that Volcanoes, Tundras, and Deserts/Arid lands are all foreign. There are very few locations on the planet wherein all 3 of these locations do not exist within 3,015 kilometers of one another, which is the total size of Wall Maria. 4.) There are Giant Redwoods dotting the landscape, and we see mountainous terrain almost all over. 5.) We know that some of the wall is bordering an ocean and that the evacuees came over from an ocean
With the information we know, we can only assume that the walls are located in central Europe, taking up areas of Germany, especially northern Germany, bordering the North Sea. This area is the only area of the world with no tundra environment and no desert environment that would also contain giant redwoods. It also matches an area that would be directly connected to both Britain and Scandinavia.
All of our knowledge of SnK’s location points towards central Europe, with the North Sea bordering the walls to the North near Germany. The walls are also not perfect concentric circles, they are uneven and could go further into one area than they go into another.
The walls could not be located in California, as Deserts are common there, or certainly would be within the 3,015 kilometers of the perimeter of the walls. They could also not be further north, in Washington, because snowfields would be common there as it gets further into Canada and so would “continents of ice” or areas of permanent frost.
Finally, if the walls were located any further to the East than central Europe, you’d again have to run into issues dealing with Tundra.
Finally, we are given flashbacks of medieval knights fighting off Titans with armor around medieval castles. We are not shown any signs of Western or American civilization.