Shetland vs sheep dog

Shetland and sheep dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
Shetland	Yes	No	No	No
sheep dog	Yes	No	No	No

As nouns, sheep dog is a hypernym of Shetland; that is, sheep dog is a word with a broader meaning than Shetland:

Shetland: a small sheepdog resembling a collie that was developed in the Shetland Islands
sheep dog: any of various usually long-haired breeds of dog reared to herd and guard sheep

Other hypernyms of Shetland include sheepdog, shepherd dog.

Shetland (noun)	sheep dog (noun)
a small sheepdog resembling a collie that was developed in the Shetland Islands	any of various usually long-haired breeds of dog reared to herd and guard sheep
an archipelago of about 100 islands in the North Atlantic off the north coast of Scotland