From Firelink Shrine, where you first set foot in Lordran upon your arrival from the Asylum, to Blighttown and the Demon Ruins, it's all there. Well, almost all there.
The image was created by redditor tettix over the course of three months, who shared it recently in the r/darksouls subreddit. It's incomplete and may never be finished since, as tettix says, "the worst parts of the game are also the worst parts to slog through illustrating." However, incomplete or not, this is one amazing piece of art.
Here's the entire illustration. Have fun clicking and zooming in!