This method is based on observation. There are 2 schools; form or known as observation and compass or known as calculation. One could not do without the other. It is best use in combination.
Door open to blade shape water 門前水路前卷：Ominous house凶宅
If you open your main door to a blade shaped or U shape water, it is said that people will leave the house and face some difficulty in life.
Consider: Erosion will happen in this part over a period of time. Land on this side will erode.
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