Within the districts established by this chapter, or amendments that may be subsequently adopted, there exist lots, structures, uses of land and structures and characteristics of use which were lawful before this chapter was adopted or amended, but which would be prohibited, regulated or restricted under the terms of this chapter or future amendment. It is the intent of this chapter to permit these nonconformities to continue until they are removed, but not to encourage their survival. It is further the intent of this chapter that nonconformities shall not be enlarged, expanded or extended or be used as grounds for adding other structures or uses prohibited elsewhere in the same district, except to the extent allowable by applicable law.