The Airport Overlay applies to properties in the vicinity of Raleigh-Durham Airport. The specific boundaries are defined on the Official Zoning Map and are imposed on property as an addition to the underlying zoning district. The boundaries generally follow physical boundaries which are identifiable on the landscape and are related to the airport noise contours as determined by the Raleigh-Durham Airport Authority. The Airport Overlay is divided into two suboverlays which are further described below: