land site vs piece of ground

land site and piece of ground both are nouns.

Word	Noun	Adjective	Verb	Adverb
land site	Yes	No	No	No
piece of ground	Yes	No	No	No

As nouns, piece of ground is a hypernym of land site; that is, piece of ground is a word with a broader meaning than land site:

land site: the piece of land on which something is located (or is to be located)
piece of ground: an extended area of land

Other hypernyms of land site include parcel, parcel of land, piece of land, tract.

land site (noun)	piece of ground (noun)
the piece of land on which something is located (or is to be located)	an extended area of land