Examples of H II regions with the candidate counterpart(s) of O-B2 stars (white star symbols). The WISE images of the W4 band (22 µm, colour maps) are shown as backgrounds. The contour levels with the corresponding data numbers (white) are marked in each panel, and the first level is adopted to indicate the H II region boundary (see Sect. 3.1). The dashed circle in each plot is the size of the H II region determined from the angular radius parameter given by the WISE H II region catalogue (Anderson et al. 2014).