The lawful use of land existing on the effective date of areas zoned or rezoned under Chapters 21.02 through 21.60, although such use does not conform to the regulations specified by Chapters 21.02 through 21.60 for the district in which such land is located, is a nonconforming use and may be continued as hereinafter provided, except that no such use shall be enlarged or increased nor be extended to occupy a greater area than that occupied by such use at the time the area is zoned or rezoned under Chapters 21.02 through 21.60 except as provided by Section 21.48.050 and except for the replacement of a mobilehome with a larger mobilehome. If any such use ceases for a period of one year, including a nonconforming mobilehome, the subsequent use of such land shall be in conformance with the regulations of Chapters 21.02 through 21.60. Should a non-conforming mobilehome be damaged or destroyed by fire, flood, explosion, or act of God, that mobilehome can be replaced if done within a period of one year following destruction of the mobilehome. A nonconforming mobilehome is a right that is transferable by the owner of the land upon which it is situated. Any billboard or outdoor advertising sign, except as otherwise permitted in any RRA, R-1, R-2 and R-3 district that is located within any RRA, R-1, R-2 or R-3 district shall be removed within seven years from and after the effective date an area is zoned or rezoned under Chapters 21.02 through 21.60.