This question has been often put to me. To analyse this, let us know about the existence of the earth. Millions of years ago, this earth was only a fire-ball. Gradually and slowly, it cooled down. It's atoms continued to be attracted towards each other because of self-magnetism. As the upper crust of the earth became cold, the gases got converted into clouds, which resulted into rains on the earth. Because of the rains, the surface of the earth cracked at different places and as such the lava under the surface burst out.
This lava got converted into mountains and valleys. Thus, mountains, plains, valleys and rivers came into existence. The water remained collected at the remaining places, which created oceans and lakes.
Because of self-attraction of atoms, the whole earth became extremely magnetic. The rivers, mountains and valleys affect the flow of these magnetic waves. This check creates different types of magnetic regions. Thus, the magnetic regions of different countries have their own impact on those countries. This has similar effect on the inhabitants also.
If we consider it minutely, the same magnetic effect shows its presence in States and cities through rivers, ponds, high and low lying land, thereby affecting the residents of those regions.
Finally, a more minute analysis has revealed that this effect takes houses and even rooms into its grip as the land is divided into pieces.
The effect decreases or increases the sphere of magnetic waves. If a long magnet is divided into two pieces, each piece has the same magnetic power. In the same manner, as we divide a piece of land into smaller units, we get separate magnetic areas. Each magnetic area has its own north-south and east-west directions.
As the decisions of the Central Government have effect on the whole of the country, those of State Government in the State, of family chiefs on the whole family and, of course, yours in the bed room, the land pieces affect similarly. This clarifies the limitation of Vastu. Even the smallest thing has its own Vastu effect because every thing is linked with or related to the earth. For example, if we have to keep the north-east corner open, we have to bear in mind that it should remain open towards the boundary wall of the part of land as also towards the house. This corner in the bedroom should be left open and the toilets should also not be constructed in this corner.
In view of the above, we have seen that the limitation of Vastu covers not only the entire earth but also the smallest piece of land having a direct bearing on our lives.