How does the poet bring out the feeling of separation between the place of his childhood and his present dwelling in "Far in a western brookland"?

Throughout the various poems of A Shropshire Lad, Housman engages in wistful reminiscence of his formative years. The Shropshire that Housman so vividly evokes is almost entirely a product of his imagination; he didn't grow up there and hardly ever visited the county. In that sense, there is inevitably an unbridgeable gap between the life he now leads and the romanticized existence of his youth.
Though the speaker of poem 52 may now live in London, his spirit still resides among the far-off Western brook land where he claims to have been born. There, he was never truly alone; he always had the poplars he knew so well for company. In his native fields, he was truly in his element; he was "known," completely at one with his natural surroundings. The contrast with London is stark. In the atomized world of the big city, he is isolated and anonymous, and when he lies down to sleep at night, he is always alone.
https://www.poetryfoundation.org/poems/58269/a-shropshire-lad-52-far-in-a-western-brookland-