Comparing 3D dust to 2D dust. Left panel: the Planck E(B − V) dust map (in blue) tracing the total dust column density integrated along the LOS. Right: the Planck E(B − V) dust map overlaid with the projection of the 3D dust map (in red) on the plane of the sky. The two maps are in excellent agreement. The 3D dust includes all dust within the L20 3D map limits (e.g., the California Nebula, which is located at a larger distance is excluded and does not show in red).