(1) Whenever it appears to the ¹[Central Government] that it is necessary to impose restrictions upon the use and enjoyment of land in the vicinity of any work of defence or of any site intended to be used or to be acquired for any such work, in order that such land may be kept free from buildings and other obstructions, a declaration shall be made to that effect under the signature of a Secretary to such Government or of some officer duly authorised to certify its orders.
     (2) The said declaration shall be published in the Official Gazette and shall state the district or other territorial division in which the land is situate and the place where a sketch plan of the land, which shall be prepared on a scale not smaller than six inches to the mile and shall distinguish the boundaries referred to in section 7, may be inspected; and the Collector shall cause public notice of the substance of the said declaration to be given at convenient places in the locality,
     (3) The said declaration shall be conclusive proof that it is necessary to keep the land free from buildings and other obstructions.