The young man's face is a map of an earlier, authentic age when beauty was natural and unadorned—not wrought from cosmetics, not stolen from the dead—and nature preserves him as evidence of beauty's true past.
Lines 5–8 contain one of the sonnet sequence's most disturbing passages: the account of wigs made from the hair of corpses. This is historically accurate (wigs were made from human hair, including that of the deceased), yet Shakespeare uses it as metaphor for the entire project of false beauty—it is necrophiliac, animated by the dead, parasitic on authentic vitality. The young man, by contrast, requires no such violation. He is 'without all ornament, it self and true,' needing neither the beautification nor the violation of other bodies. His authenticity is defined negatively: he does not steal, rob, or animate the dead. His beauty is self-sufficient, requiring nothing external, a stark contrast to the 'bastard signs of fair' that depend on artifice and corpses.
The final couplet's image of nature storing the young man 'as for a map' transforms him from person to artifact. He becomes a kind of living museum, a preserved specimen of an extinct type: the authentically beautiful. Nature does not merely love him; she archives him, keeps him as evidence against false art. This is simultaneously honoring and disturbing: to be preserved as a map is to be fixed, static, valuable only as a historical record rather than as a living being. The young man is thus positioned as the last living representative of an age of authentic beauty, and his beauty's value depends partly on its rarity and historical distance. He shines brightest against the darkness of false modernity.
Like someone whose natural beauty seems to come from a different era, untouched by trends and filters. They're like living proof that real beauty existed before Instagram, a reminder of what genuine looks like without any artificial enhancement.