A lawful use of land, buildings or structures existing at the effective date of this chapter may be continued on the lot or in the structure although it may not conform to this chapter, and any such structure may be restored or repaired in the event of partial destruction thereof; provided, however, that none shall be enlarged, extended, relocated, converted to another use or altered except in conformity with this chapter, except as permitted below. Land on which a nonconforming use or structure is located and any nonconforming lot shall not be subdivided so as to be made more nonconforming.