Effect of BDC priors on the distance estimation for a source located at ℓ = 20.66°, b = −0.14°,  and v_LSR = 56.2 km s⁻¹. For panel a we set and , for panel b we set and , and for panel c we set and . Coloured lines show the probabilities of the priors for kinematic distances (blue solid line), latitude probability (orange dotted line), spiral arms (red dashed line), and associations with parallax sources (green dash-dotted line). The black solid line shows the combined distance PDF. The red-shaded areas show the distance ranges for which the source would be associated with individual Galactic features. Black circles and white diamonds indicate the first and second choice for the distanceestimates, with the horizontal bars showing their corresponding uncertainties. The boxes above the panels list the resulting distances, their uncertainties, and estimated probabilities.