All lawful uses of land, buildings, signs or other structures
existing on the effective date of this chapter may be continued, altered,
restored, reconstructed, sold or maintained in accordance with the
provisions of this chapter.
Whenever a nonconforming use has been changed to a conforming
use, such use shall not thereafter be changed to a nonconforming use.
A nonconforming use may be changed to another nonconforming use only
by special exception. Whenever a nonconforming use has been changed
to a more restricted classification or to a conforming use, such use
shall not hereafter be changed to a use of less-restricted classification.