From and after the effective date of this chapter, no structure shall be erected, constructed, enlarged, reconstructed, or altered and no structure or land shall be used or occupied for any purpose nor any manner which is not in conformity with this chapter, except as specifically provided herein. Any structure or use existing upon the effective date of the adoption of this chapter shall be considered a nonconforming use subject to the rights and limitations specified in Articles II, III and IV of this chapter.