Section 2(1a)(a) in The Calcutta Improvement Act, 1911
(a)"the Board" means the Board of Trustees for the improvement of Calcutta, constituted under this Act;(aa)[ "Building line" means a line (in rear of the street alignment) up to which the main wall of a building abutting on a projected public street may lawfully extend] [Clause (aa) inserted by Ben. Act 3 of 1915.];