Sustainability considerations should include the environmental condition of the land, for example discounting land built on flood planes, toxic land or landfill sites.
Dylai ystyriaethau cynaliadwyedd gynnwys cyflwr amgylcheddol y tir, er enghraifft, diystyru tir a adeiladwyd ar orlifdir, tir gwenwynig neu safleoedd tirlenwi.