Astrology & Vaastu are interrelated. Astro-vastu

 Your birth chart is a map.

1st house: EAST
2nd & 3rd: North-East
4th house: NORTH
5th & 6th: North-West
7th house: WEST
8th & 9th: South-West
10th house: SOUTH
11th & 12th: South-East

Sun prefers East
Saturn prefers West
Mercury prefers North
Mars prefers South

Moon: North-West
Venus: South-East
Jupiter: North-East
Rahu: South-West

Directions and your birth chart is used in Vaastu to channelize your energy.