As used in this article:
(a) "Exterior architectural features" include the architectural character and general composition of the exterior of a structure, including, but not limited to, the kind, color and texture of the building material and the type, design and character of all windows, doors, light fixtures, signs, other appurtenant elements and natural features when they are integral to the significance of the site, all of which are subject to public view from a public street, way or place.
(b) "Historic district" is a geographically definable area possessing a significant concentration, linkage or continuity of sites buildings, structures or objects united historically or aesthetically by plan or physical development.
(c) "Historic landmark" is a site, building, structure or object designated as a "Landmark" either on a national, state or local register.
(d) "Historic site" is the location of a significant event, a prehistoric or historic occupation or activity, or a building or structure, whether standing, ruined or vanished, where the location itself possesses historical, cultural or archaeological value regardless of the value of any existing structure.