Left panel: view of the CH₃OH maser features detected around S231 (Table A.4). Right panel: zoom-in view of group A1. Same symbols as in Fig. 2. The arrow indicates the direction of the blue-shifted lobe of the H₂-outflow (PA_out = 133°; Ginsburg et al. 2009).The dashed line is the best linear fit of the CH₃OH maser features of group A (°), while the dotted line is the best linear fit of the CH₃OH maser features of groups B, C, and D (°).