Within the districts established by this chapter and later amendments hereto, there exist nonconforming situations: lots, buildings and structures, uses of land and uses of buildings or structures and land in combination which were lawful before this chapter was passed and amended, but which would be prohibited 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 upon, expanded or extended, except as hereinafter provided, nor be used as grounds for adding other structures or uses prohibited elsewhere in the same district.