Noise zones of a strategic noise map type C night of Charente

Noise zones are geometrical components of the strategic noise map. For Type A maps (CBSTYPE), each noise zone is generally bounded by 2 isophone curves (Lden 55-60, 60-65, 65-70, 70-75 and Ln 50-55, 55-60, 60-65, 65-70) or the lower limit isophone curve (Lden > 75, Ln > 70). For type C maps (CBSTYPE), each noise zone is bounded by the lower limit isophone curve (Lden > 68 or 73, Ln > 62 or 65).