"My heart's in the Highlands":

This is the central metaphor. It's not literal, but rather a powerful way to express the speaker's deep emotional attachment and longing for the Highlands, even when physically away.

"Chasing the wild-deer" and "following the roe":

These images evoke a sense of freedom, adventure, and the wildness of the Highlands, further emphasizing the emotional connection the speaker has with the land.

The imagery of the Highlands (mountains, straths, forests, torrents):

These descriptions are more than just scenery; they represent the speaker's ideal, a place of beauty, wildness, and perhaps a sense of belonging.

Anaphora:

The repeated phrase "My heart's in the Highlands" acts as a powerful rhetorical device, creating a sense of urgency and emotional intensity. It reinforces the speaker's unwavering loyalty and connection to the Highlands, even when physically separated. 

Imagery:

The poem uses descriptive language to evoke a strong sense of the Highlands' natural beauty and wildness. The speaker describes "chasing the wild-deer, and following the roe," which paints a picture of the landscape and its inhabitants. 

Parallelism:

The repetition of similar sentence structures, like "My heart's in the Highlands, wherever I go" and "My heart's in the Highlands, a-chasing the deer," creates a rhythm and flow that emphasizes the speaker's unwavering sentiment, according to a post on Literature Stack Exchange. 

Rhyme and Rhythm:

The poem's use of a regular rhyme scheme and meter contributes to its memorability and lyrical quality, making it a song as well as a poem. The repetition of "Highlands" and "go" creates a musical effect that reinforces the poem's emotional core.