Results from simultaneously fitting the emission of nine unblended transitions of CH₃OCHO with XCLASS (see Table 1 and Sect. 3 for details). Upper panels: maps of column density (left) and rotational temperature (right). Lower panels: maps of VLSR (left) and line width (right). The maps are shown inside the region of core A1 where the column density of CH₃OCHO is higher than 3 × 10¹⁶ cm⁻² (red contour). The magenta contour is the 5σ threshold of the ALMA 1.4 mm continuum emission. The black contours reproduce the JVLA A-Array 1.3 cm continuum (plotting the same levels as in the upper panel of Fig. 4). We label with “A1N”, “A1N-W”, “A1M” and “A1SW” four regions of interest of the core A1. In the FWHM map, the two white contours correspond to a level of FWHM = 7 km s−1, and delimite the two regions of prominent line widths LW-CS (to the N) and LW-ER (to the S). The yellow squares give the absolute positions of the 6.7 GHz CH3 OH masers, determined via multi-epoch, sensitive EVN observations. Square area scales with the maser intensity. After correcting for the apparent motion between the EVN and ALMA observations, maser absolute positions are accurate within a few milliarcsecs. In the VLSR map, 6.7 GHz masers are represented with colored squares to recognize their VLSR, and black arrows show the proper motions of the masers in the cluster A1SW with respect to the barycenter of the masers in the cluster A1N (see Table B.1). The amplitude scale for proper motion is shown in the lower-left corner of the plot.