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The outer surface, shown on Peterborough Airport Zoning Plan No. 15-006 89-43, Sheets 1, 2, 3, 4, 5, 6, 7, 8 and 9, dated December 29, 1989, is an imaginary plane established at a constant elevation of 45 m above the elevation of the airport reference point, except that, where that plane is less than 9 m above the surface of the ground, the outer surface is located at 9 m above the surface of the ground.
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