Why do North Indian and South Indian kundalis look different?

they are two drawings of the same chart — the North style fixes the houses, the South style fixes the signs.

The North Indian chart is a diamond inside a square. The top central diamond is always the first house (lagna), and houses run anticlockwise; the sign numbers written in each box change from person to person.

The South Indian chart is a square grid of twelve boxes around an empty centre. Each box is always the same sign — Pisces top-left, then Aries, Taurus and so on clockwise — and the lagna is marked with a line or “La/Asc” in whichever box it falls. East Indian charts use a third layout.

The planets, degrees and predictions are identical whichever style you use; only the picture differs. Pick the one your family or astrologer reads comfortably. Many apps, including birth-chart tools, let you switch between them.

Source: modern practice · Same chart, different drawing

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