Feng Shui Pa Gua

巽读为训. 代表长女和东南方. 命卦为2. 木.
离代表三女和南方. 命卦为3. 火.
坤代表母亲或女主人和西南方. 命卦为1. 土.
震代表长子和东方. 命卦为8. 木.
艮读为更. 代表小儿子和东北方. 命卦为6. 土.
坎代表二儿子和北方. 命卦为7. 水.
乾代表父亲或男主人和西北方. 命卦为9. 金.
兑读为对. 代表小女和西方. 命卦为4. 金.

From here, we can see why in term of feng shui, our house has to be square and not missing any corner because for instance, if the east part of your house goes missing, your eldest son will go missing i.e. you have no eldest son.