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The outer surface, shown on St. Catharines Airport Zoning Plan No. 26-047-81-67, Sheets 1 to 9, dated March 30, 1984, is an imaginary surface located at a common plane established at a constant elevation of 45 m above the assigned elevation of the airport reference point except where that common plane is less than 9 m above the surface of the ground, the imaginary surface is located at 9 m above the surface of the ground.
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