The earth elements gives us gravitational energy, its physical attributes creates shapes, bodies and structure. The earth element provides stability in a structure. One fourth of your plot has a strong hold on the earth element. The part is half of the south and west direction.
The southern and western corners are extremely essential to harness the earth element. Vaastu defect is created in the area where the earth element is missing, for example if basements are digged in southwest areas a big vaastu defect is created. Digging a well or an underground water tank in the south west of your plot could also cause vaastu defects.
If the building structure is made in the northern and eastern parts of the plot, and the southern and western direction remain vacant as a result the plot is deprived of the earth element. One should not give water slops towards the southwest. Heavy structure or elevation towards the southwest is prosperous. The earth element is integaral part of vaastu. Hence it has to be balcanced.