The lawful use of land, buildings or structures existing at the time of the adoption of the ordinance codified in this title, although such use does not conform to the provisions of such ordinance, may be continued. If such nonconforming use is abandoned for a period of six months or more, any further use of such land, building or structure must be in conformity with the provisions of this title. The mere presence of a building or structure shall not be deemed to constitute the continuance of a nonconforming use unless such structure is actually continuously occupied and used in the nonconforming manner.