Except as hereinafter provided, no building or structure or part thereof and no lot or land or part thereof shall hereafter be used except for a purpose specifically permitted by the provisions of the Table of Use Regulations for the district in which such building or structure, lot or land is located on the Zoning Map.

Any lawful use that does not conform to the use regulations of this chapter shall be deemed a nonconforming use.

A use for which a special permit use has been authorized by the Planning Board shall be deemed a conforming use.

A use authorized by a variance from the use regulations of this chapter granted by the Zoning Board of Appeals shall be deemed a nonconforming use.

Except as hereinafter provided, no building or structure or part thereof shall hereafter be erected, structurally altered, enlarged, rebuilt or moved except in conformity with the provisions of the Density Control Schedule for the district in which such building or structure is located on the Zoning Map. No building shall:

Any lawful existing building or structure that does not conform to such Density Control Schedule shall be deemed a nonconforming building or structure, irrespective of the use of which it is part.

A building or structure or part thereof authorized by variance from the Density Control Schedule granted by the Zoning Board of Appeals shall be deemed a nonconforming building or structure or part thereof.

No part of a yard or lot area required in connection with any building shall be included as a part of a yard or lot area for another building.

No off-street parking or loading space shall be so reduced in area that it does not meet the requirements of this chapter.

The required lot or yard for an existing building or structure shall not be diminished below the minimum requirements of this chapter unless a variance is granted pursuant to this chapter.