The lawful use of land existing upon the effective date of this article, although such use does not conform to the provisions hereof, may be continued, subject to the provisions hereof. Such use may be extended throughout such portions of the buildings as are arranged or designed for such use, provided no structural alterations, except those required by law or ordinance, are made therein. If such nonconforming building is voluntarily removed, the future use of such premises shall be in conformity with the provisions of this article. In the event a nonconforming use of any building or premises is discontinued for a period of one (1) year, the use of the same shall thereafter conform to the provisions of the district in which it is located.