Face-on view of the number of Gaussian fit components for the BDC results obtained with (left) and without (right) the spiral arm prior. The values are binned in 10 × 10 pc cells and are summed up along the z_gal axis. The position of the Sun and Galactic centre are indicated by the Sun symbol and black dot, respectively. When displayed in Adobe Acrobat, it is possible to show the spiral arm positions and the grid.