Within the districts established by this Part or any amendment that may later be adopted, there exists lots, uses of land, structures and uses of structures and land in combination which were lawful before this Part was passed or amended, but which would be prohibited, regulated or restricted under the terms of this Part or future amendments. It is the intent of this Part to permit these non-conformities to continue until they are removed. It is further the intent of this Part that non-conformities shall not be enlarged upon, expanded or extended, nor be used as ground for adding other structures or uses prohibited elsewhere in the same district.