¹³CO (1 − 0) maps (contours) overlaid on the far-infrared images (gray). The thick contour in each map denote the 50 per cent level of the maximum intensity. For each map, the interpolation is performed upon a grid with 100 × 100 pixels. For all the regions, it is guaranteed that the pixel size is far smaller than the mapping step. And in each panel, the black cross indicates the central position (where the maser locates), the square indicates the radio continuum source (plausible Ultra- or Hyper-Compact Hii regions, if they exist), the dashed ellipses indicate the identified cores if there are overlapped multiple cores.