Plummer profile parameter correlations. Contours 1.5 and 10 are drawn for Plummer profile fits obtained from WFCAM A_V map (black lines) and Herschel column density map (red lines). In each case we fix one of the three Plummer parameters (ρ_c, R_flat or p) and change the others. The axes show parameter values relative to those of the (see Table 1 for the precise values of the parameters).