He Tu

When a feng shui book overlays a floor plan with a 3×3 grid, or a flying-star chart drops the numbers 1 through 9 into its nine cells, that frame is not the author’s invention. It is the Lo Shu square (洛书, Luoshu, “the writing of the Luo River”) — and beside it stands an older companion, the He Tu (河图, Hetu, “the diagram of the River”), which pairs the same numbers with the five phases. Cited together as one phrase — he tu luo shu (河图洛书) — the two are the numerical layer beneath the more famous charts: the post-heaven trigrams carry Lo Shu digits as their addresses, and every flying-star or nine-palace diagram is drawn on the Lo Shu grid. This page lays out both figures: the legend and the earliest text, the birth and completion numbers of the He Tu, the magic square of the Lo Shu, how the trigrams plug into it, where the two charts surface in practice, and how they differ.