We've been uncovering Tamriel since way back in the '90s with Arena and Daggerfall, but you couldn't really make out a detailed map with either game. The land was procedurally generated and each city was essentially a copy-and-paste with a slightly different layout. The world wasn't as distinct as later releases like Morrowind and Skyrim.
But these were limited to single provinces eras apart - The Elder Scrolls Online, meanwhile, is one big game that lets us visit Vvardenfell, the Summerset Isles, Elsweyr, Shadowfen, Wrothgar, Riften, Windhelm, Cyrodiil, and the Gold Coast. So one fan is puzzling together all of its spots to make Tamriel's most detailed map yet.
It's giant and you can zoom into any spot and find cities, landmarks, terrain, rivers, mountains, forts, and other little details. Take Windhelm. For context, not all of Skyrim is present in ESO - instead, there's Windhelm, the Rift, Markarth, and Solitude, as the province is divided. Markarth is ruled by Reachmen, Windhelm and Solitude are opposing capitals with their own High Kings, and the Rift is part of Western Skyrim. Zooming in, we can see Fort Amol, Ivarstead, Voljar's Meadery, and even Lake Honrich.
Daggerfall meanwhile boasts the Doomcrag, Shornhelm, Camlorn, and Wayrest, while we can see part of Hammerfell to the south with Sentinel, Lek's Blade, Bergama, and the Alik'r Desert. If you want a comprehensive map of Tamriel that lets you see just where every slice of its lore fits into place, Bengamey_974's work is perfect.
However, they clarified that they didn't use ESO's world map, but instead "the individual zone maps". In essence, they stitched these together while making their own tweaks so that it would all flow coherently. That meant separating Stonefalls from the Rift to recreate the Velothi mountains, while Cyrodiil had to be scaled down. The Systres Archipelega was also shrunk for lore reasons, as on the map, it's nearly the same size as the much larger Summerset Isles.