This article is intended to limit the number and extent of nonconforming uses by prohibiting their enlargement, their re establishment after abandonment, and the alteration or restoration after destruction of the structures they occupy. While permitting the use and maintenance of nonconforming structures, this article is intended to limit the number and extent of nonconforming structures by prohibiting their being moved, altered, or enlarged in a manner that would increase the discrepancy between existing conditions and the standards prescribed in this article and by prohibiting their restoration after destruction.