Within their zoning ordinances, communities may use overlay zones to protect particular natural or cultural features, such as historic districts, steep slopes, waterfronts, scenic views, agricultural areas, aquifer recharge area, wetlands, watersheds, or downtown residential enclaves. Overlay zones build on the underlying zoning, by establishing additional or stricter standards and criteria; the standards of the overlay zone apply in addition to those of the underlying zoning district. Overlay zoning can be an effective tool for communities to use in protecting specific resources from development pressures. For example, an overlay zone can be instituted for a specific neighborhood to preserve its character and design by encouraging new construction, and additions to existing buildings, that are compatible with the neighborhood's building types and character. An overlay zone can also be designated in areas to promote mixed-use development, such as near community centers. Additionally, municipalities can use overlay zones in existing low density, single use areas to encourage mixed-use or higher density development. An overlay zone may be used near a certain intersection or street which is served by transit, in order to increase the amount of housing to support that transit corridor. Overlay zones could also be used to allow affordable housing as a use by right in areas selected by the community, regardless of the current zoning. (http://www.co.tompkins.ny.us/planning/vct/tool/overlayzones.html#)