Any lawful use occupying any building, structure, lot or land at the time of the effective date of this chapter, or any amendment thereof, which does not comply, after the effective date of this chapter, or any amendment thereto, with the use regulations of the district in which it is situated, may be continued in the building or structure or upon the lot or land so occupied, to the extent existing at the time it became nonconforming, except as otherwise provided for in this article.