Index values calculated for the OB population by INDICATE when applied to the entire stellar catalogue, (top panel); and OB sub-sample, (bottom panel; see text for details). Positions of the Tr14, Tr15, Tr16, TC, Bochum 11 and M (sub-) clusters are overlaid as black ellipses. The borders of our designated NW and SE regions are marked with blue dotted and green dashed lines respectively. Coloured triangles represent OB stars with an index value above the respective significance thresholds. Grey triangles are OB stars below the respective significance thresholds.