Sketch of a distribution of core layers within the Gaussian beam of the telescope (black ring). Here, we assume three different core components 1, 2, and 3, centered at the middle of the beam with different source sizes, excitation temperatures, velocity offsets etc. indicated by different colors. Additionally, we assume that all core components have the same distance to the telescope, i.e., all core layers are located within a plane perpendicular to the line of sight. Furthermore, we assume that this plane is located in front of a background Layer 4 with homogeneous intensity over the whole beam. Core components do not interact with each other radiatively.