parkland vs piece of ground

parkland and piece of ground both are nouns.

Word	Noun	Adjective	Verb	Adverb
parkland	Yes	No	No	No
piece of ground	Yes	No	No	No

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

parkland: a large area of land preserved in its natural state as public property
piece of ground: an extended area of land

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

parkland (noun)	piece of ground (noun)
a large area of land preserved in its natural state as public property	an extended area of land