Any nonconforming lot, building, structure or use legally existing at the time of adoption of this chapter, or which is created whenever a district is changed by amendment hereafter, may be continued, altered, reconstructed, sold, or maintained, even through it does not conform to the regulations of the district in which it is located, except as provided below. It is the intent of this chapter to permit these nonconformities to continue until they are removed, discontinued, or abandoned.