Position of the H II regions detected in galaxy NGC 6946. Filled circles are the regions considered for the main north arm. Filled squares, filled diamonds, and filled triangles are the regions considered for the NS arm, the south arm, and the SN arm. Two secondary satellite arms, not included in the study, are represented by the dashed lines. The inner dot-dashed line is the Ω − κ/3 resonance, and the outer dot-dashed line is the Ω − κ/4 resonance. North is at the top and east is left.