An Anons Guide To Find The Depth Maps

Den of Darkness: Handed to you by Shang in Outer Crossroads (where you fought Oliver).

Den of the Dead: In the hallways leading from Outer Crossroads to Ruined City Center (has the Hermes Vestige A in it and also a great early-game unga bunga weapon in a chest)

Town of Sacrifice: Dried-up Trenches, by the second mistle

Swirling Flood: Handed by Shang as part of his questline

Flood of Impurity: After beating Miku and Despot and lowering the ladder via the statue, in the hallway leading to Anal Rodeo

Cliffs of Rust: Handed to you by Self-Important Revenant as part of his questline near the second mistle in Dried-up Trenches

Arachnid Grotto: Meet Gustav at the first mistle of Dried-up Trenches, do his quest (documents in Parking Garage, Snow Level and Anal Rodeo), then meet him at third mistle of Ashen Caverns, he will hand you the map

Silent White: Handed to you by Shang as part of his questline, after running his errand in Swirling Flood

Rocky Ruins: The tough one. You need to finish the questlines of Self-Important Revenant, Joyous Revenant and Richard, once you've done all their busywork and killed Mido, go to the blood spring in the starting dungeon, where Richard will hand you the map. This one has the Scout Vestige Core in it.

Misty Ruins: Crypt Spire, right before the elevator, explore the area thoroughly. Among the rewards are: A healing upgrade, the Mistle
Root (Coiled Sword Fragment/Aged Feather/Infinite Vivifier) and the map

Zero District: After the Queen's Knight Reborn, on the way to the final dungeon, can't miss it.

Void District: Near the Eastern ladder in the final dungeon