Vastu is the science of architecture and town planning. Vastu deals with every aspect of building planning including choosing the plot, looking for the slope of the land, scope of sunlight and water, the position of gate, window, fireplace, kitchen, bedroom etc.
It is a complete science on home building and building construction. No one rule on building is out of place. Each rule described in vastu has specific implications.
A comparable science is Feng Shui of China, but has differences in the form of directions and positions of objects and rooms. It may be because of the difference in physical properties of the geographies.
The four elements of Vastu are
Bhoomi — earth or the site
Prasada — walls and other features
Yaana — Vehicles
Vastu sastra (the science of architecture and town planning) gives minute directions regarding the selection of plot, positions of rooms and features, position of well and the general characteristics of each building.
Vastu shastra is fine tuned knowledge of geometry and energy manifestations.