House system — Astrology glossary

A house system is a method for dividing a natal chart into twelve houses, the life areas planets fall into. Different systems, such as Placidus, Whole Sign, Koch, and Equal, split the sky using different mathematics, so they can place a planet in different houses for the same birth data. It matters because the chosen system can change which area of life a planet is read as governing, especially near a house boundary. For example, a planet that lands in the tenth house under Placidus might fall in the ninth under Whole Sign, shifting its meaning from career toward travel or belief. Astrologers often pick a system by tradition or testing, and the choice remains one of the field's longest-running debates.