The 'vacant land" has been defined in Section 2 (q) as follows: "vacant land ' means land, not being land mainly used for the purpose of agriculture,, in an urban agglomeration, but does not include [i] land on which construction of a building is not permissible under the building regulations in force in the area in which such land is situated, 731 [ii]in an area where there are building regulations, the land occupied by any building which has been constructed before or is being constructed on, the appointed day with the approval of the appropriate authority and the land appurtenant to such building; and [iii] in an area where there are no building regulations, the land occupied by any building which has been constructed before, or is being constructed on, the appointed day and the land appurtenant to such building; Provided. . . . " The "land appurtenant ', in relation to any building, has been defined in Section 2(g) 'as follows: " land appurtenant", in relation to any building, means [i] in an area where there are building regulations, the minimum extent of land required under such regulations to be kept as open space for the enjoyment of such building, which in no case shall exceed ' five hundred square metres; or [ii] in an area where there are no building regulations, an extent of five hundred square metres contiguous to the land occupied by such building, and includes, in the case of any budding constructed before the appointed day with a dwelling unit therein, an additional extent not exceeding five hundred square metres of land, if any, contiguous to the minimum extent referred to in sub clause [i] or the extent referred to in sub clause [ii], as the case may be".