Vaastu Shastra is part of the Vedas and originates in the Stapatya Veda which is part of the Atharva Veda. The first official treatise on Vaastu, the Kasyapa Silpa, was attributed to Sage Kasyapa. The principles used in the architecture, structure, and the construction of temples in the Vedic period used the guidelines of Vaastu.
Vaastu means dwelling and Shastra means text or knowledge. Similar to Ayurveda, it is a science that is based on the five natural elements – earth (bhumi), water (jal), fire (agni), air (vayu), and space (akash) and the energy flow from the sun.
Vaastu takes into consideration Ayadi calculation where it considers a building (such as a palace or temple for which it was used in ancient times) a living being and the designers were very careful about the impact that the physical structure would have on the individuals living inside. The Ayadi calculation/formula was used to improve the prosperity and well-being of the inhabitants.
Therefore in Vaastu, Aaya (income) from the eight different directions is considered important as luck/income energy could come if there was a symbiotic connection established between architecture and nature. The eight “Aayas” documented are:
Gaja or north
Kaka or north-east
Vrusha or west
Khara or north-west
Dhwaja or east
Dhumra or north-east
Simha or south
Svana or south-west
The entrance or front door of the building should be facing the native side of "aaya" and not the opposite. So for example, if the building is dhwaja/east facing, the entrance door should not be on the west side or therefore facing west.
The above concept of Aaya Prakaran is the most important in Vaastu while constructing your home or place of business as it will help to eliminate negativity and increase positive energy.