This section establishes separate districts, each of which is an appropriate area for the locations of the uses which are permitted in that district. It is necessary and consistent with the establishment of those districts, that non-conforming buildings, structures, and uses not be permitted to continue without restrictions. Therefore, the purpose of this article is to provide for the regulation of non-conforming buildings, structures, and uses and to specify those circumstances and conditions under which those non-conforming buildings, structures and uses shall be permitted.