Vāstu Śastra represents a body of ancient concepts and knowledge to many modern architects, a guideline but not a rigid code. The square-grid mandala is viewed as a model of organisation, not as a ground plan. The ancient Vāstu Śastra texts describe functional relations and adaptable alternate layouts for various rooms or buildings and utilities, but do not mandate a set compulsory architecture. Sachdev and Tillotson state that the mandala is a guideline, and employing the mandala concept of Vāstu Śastra does not mean every room or building has to be square. The basic theme is around core elements of central space, peripheral zones, direction with respect to sunlight, and relative functions of the spaces.