a zone or district created by the local legislature for the purpose of conserving natural resources or promoting certain types of development
An overlay zone is a mapped zone that imposes a set of requirements in addition to those laid out by the underlying zoning regulations. Overlay zones typically address special features or conditions that may pertain to several distinct districts, such as historic areas, wetlands, and downtown residential enclaves.
A set of zoning requirements that is superimposed upon a base zone. Overlay zones are generally used when a particular area requires special protection (as in a historic preservation district) or has a special problem (such as steep slopes, flooding or earthquake faults). Development of land subject to overlay zoning requires compliance with the regulations of both the base and overlay zones.