Illustration of the simple mock data in the Galactic plane. The true dust density decreases exponentially from the Galactic center (GC) in all directions. The observer is at the Sun. Region 1: in addition to the main dust variations there is a cloud between 3 and 3.5 kpc, 200 stars are observed here. Region 2: no stars are observed. Region 3: 100 stars are observed here (there is no cloud). Stars are drawn from throughout regions 1 and 3, their attenuations calculated, and observational noise added.