Within the zones established by this title, there exist lots, parcels, structures or uses that were lawful before June 18, 1956, or before the adoption of this chapter (date of adoption), but that now are prohibited or restricted by this title. It is the intent of this chapter to provide for the regulation of such nonconformities, and to specify the circumstances and conditions under which they may continue to exist. Further, it is the intent of this chapter to specify those circumstances and conditions under which those nonconforming uses, buildings and structures that adversely affect the maintenance, development or use and assessed value of other property in the zoning classification in which they are located, in order that they shall be gradually eliminated.