The differences between the two methods lie in the birth chart grid. The North Indian Chart, drawn as a diamond-shaped house within a rectangular grid, runs counter-clockwise in the 12 house or bhava. In the South Indian birth chart, the rectangular grid goes clockwise from any house or bhava.
In the North Indian chart, the zodiac sign symbol is numbered, with Aries being 1, Taurus being 2, and so on, and the ascendant house is always at the top of the grid, numbered per the sign. In the South Indian chart, Aries is always in the 2nd House from the top left of the rectangular birth chart grid, and the Ascendant House can be anywhere in the clockwise sequence depending on the time of birth
Beyond these differences, the two methods follow the same Vedic Astrological principles