General application. All buildings and structures erected hereafter, all uses of land or buildings established hereafter, all structural alterations or relocations of existing structures occurring hereafter, and all enlargements of, additions to, changes in and relocation of existing uses occurring hereafter shall be subject to all the regulations of this chapter which are applicable to the districts in which such buildings, structures, uses or land is located. Existing buildings, structures and uses which do not comply with the regulations of this chapter shall be allowed to continue, subject to the provisions of § 340-3.4 of this chapter relating to nonconformities.