Selected regions and the dark clouds (this work) overlaid on the I_Hαmap of Sh 2–27. The dashed circle with a radius of 1°.2 is chosen to estimate the off-region used in RM_sh2–27estimation (see Sect. 5.3). The dashed box is used for the SF calculations. Each side of the box is ~6°. Contours from the CO emission map of Dame et al. (2001) are overlaid on the H II region to display the structure of the dark clouds. The plus sign represents the location of ζ Oph at (l, b) = (6°.3, +23°.6). The greyscale range is 0–2000 dR.