Since the answer is intertwined with the lines of the poem, this is a little awkward to answer. Let's start by defining a couple of things. Hardy (1840-1928) is writing about a drummer boy in the British army during the British-Afrikaner Anglo-Boer War (1899-1902) that was fought on South African soil, in part on the Karoo desert, primarily around Prince Albert.
Hardy appropriately sprinkles lines with Afrikaner words for physical features in the Karoo:
- a kopje, as in "kopje-crest" is a "little hill."
- the "crest" is its top, or peak.
- the "veldt" is the grassy flatland plains of South Africa; they span for acres and acres, or hectares and hectares. Kopjes rise without warning from the veldt, looking like so much popcorn sprinkled about; this is how the kopje "breaks the veldt around."
- the "foreign constellations" are, of course, Southern Constellations, which are different from Northern ones, though some of these "strange stars" are shared in common between the two hemispheres.
- the "mound" is a Classical allusion to an ancient burial mound such as Greek heroes were given; it is a signification of respect and honor to the war-fallen drummer boy.
- the "strange-eyed constellations" of the Southern skies will, now, forever be his ruling astrological signs replacing Northern signs of his native Wessex home.
With this understanding in mind, we can now answer "How does the South African landscape become Hodge's home?" Hodge becomes one with the crest of a kopje in the midst of the unknown veldt surrounded by the wilderness of "that unknown plain." His unburied body, lying where it fell in battle, "Uncoffined," will send its decomposition to the soil to become part of the earth that eventually will nourish a near-by South African tree (none grow atop kopjes). Southern stars will be the canopy, or curtain, over his head as they govern his eternal path, once governed by Northern stars, as he rests atop his hero's funeral "mound" beneath the "strange-eyed stars" of his eternity.