Relative orientation parameter ξ, defined in Eq. (3), calculated for the different N_H bins towards the sub-regions of Vela C as defined in Hill et al. (2011) and illustrated in Fig. 2. The values ξ> 0 and ξ< 0 correspond to the magnetic field being oriented mostly parallel or perpendicular to the iso-N_H contours, respectively. The black dashed line and the values of C_HRO and X_HRO correspond to the linear fit introduced in Eq. (5). The grey line is ξ = 0, which corresponds to the case where there is no preferred relative orientation.