Improvements to land that merge with the land and therefore become part of the land value . For example, filling and drainage. In established areas these are improvements that are difficult to identify.

Under the Valuation of Land Act 1916 (NSW) (s4 definitions), invisible improvements such as excavation are part of the land improvements and becolme part of land value:

"Land improvements" means:
(a) the clearing of land by the removal or thinning out of timber, scrub or other vegetable growths,
(b) the picking up and removal of stone,
(c) the improvement of soil fertility or the structure of soil,
(d) the restoration or improvement of land surface by excavation, filling, grading or levelling, not being works of irrigation or conservation,
(d1) without limiting paragraph (d), any excavation, filling, grading or levelling of land (otherwise than for the purpose of irrigation or conservation) that is associated with:
(i) the erection of any building or structure, or
(ii) the carrying out of any work, or
(iii) the operations of any mine or extractive industry,
(e) the reclamation of land by draining or filling together with any retaining walls or other works appurtenant to the reclamation, and
(f) underground drains.