All lawful uses of land, buildings or other structures may be continued, altered, reconstructed, changed, sold or maintained without being in violation of this chapter, even though such use may not conform to the use and/or dimension regulations of the district in which it is located. When existing uses do not conform to the regulation established for the district in which located, such uses become nonconforming in terms of this chapter, and such nonconforming uses or structures must comply with the following.