Why is Feng Shui considered a science?

The science of Feng Shui remains squarely rooted in architecture, astronomy, physics, and design. According to the ancient "keepers of the knowledge" from the Taoist tradition, the evolutionary roots of Chinese Wholistic Medicine came into being at least  8,000 years ago through the first two of the Eight Branches of the Tao Healing Arts. Over the centuries the other six branches evolved into a unified way of life.

Feng shui is one of the Five Arts of Chinese Metaphysics, classified as physiognomy (observation of appearances through formulas and calculations). The feng shui practice discusses architecture in metaphoric terms of "invisible forces" that bind the universe, earth, and humanity together, known as qi/chi. 

Historically, Feng Shui was widely used to orient buildings—often spiritually significant structures such as tombs, but also dwellings and other structures—in an auspicious manner. Depending on the particular style of feng shui being used, an auspicious site could be determined by reference to local features such as bodies of water, stars, or a compass.

Qi rides the wind and scatters, but is retained when encountering water.^[1]

Feng shui was suppressed in mainland China during the cultural revolution in the 1960s, but since then has increased in popularity.

"Physician, heal thyself."

Science is definited as follows:

1. The observation, identification, description, experimental investigation, and theoretical explanation of phenomena. b. Such activities restricted to a class of natural phenomena. c. Such activities applied to an object of inquiry or study.
2. Methodological activity, discipline, or study: “I’ve got packing a suitcase down to a science.”
3. An activity that appears to require study and method: the science of purchasing.
4. Knowledge, especially that gained through experience.

Feng Shui uses observation, repeatable calculations and methodologies, and is based on the study of the environment around, both inside and out. Kan Yu, the original name for Feng Shui, means “Raise the head and observe the sky above. Lower the head and observe the environment around us.” More precisely, Feng Shui is the scientific study of the natural and built environment. All in all, it is the study of environmental effects on people.

Just as acupuncture was not accepted by western medicine until several years ago, the study of Feng Shui is just now becoming popular. While there are many variations of Feng Shui that would not withstand the scrutiny of common sense, traditional Feng Shui has logical explanations for all of its methodologies.

The I Ching (or Yi-Jing)

The Book of Changes, or Yi Jing (known in the West as I-Ching), is China's oldest philosophical text. Its origins are lost in the mists of time, but scholars believe the first compilation was done early in the Zhou Dynasty (1022 BC to 256 BC). Based on a divination system using the eight trigrams (groups of solid and broken lines), permutations of 64 pairs of trigrams were worked out. Over the ages short, memorable commentaries were added. For example:

Lü / Treading [Conduct]
Above CH'IEN THE CREATIVE, HEAVEN
Below TUI THE JOYOUS, LAKETREADING.
Treading upon the tail of the tiger. It does not bite the man. Success."

The Book of Changes charts the movements and developments (hence, 'changes') of all the phenomena in the universe. Many regard it as a complete system of philosophy in itself. Emperors, statesmen and generals throughout Chinese history consulted it.

Revered by Confucius, the Book of Changes was included in the five classic texts of Confucianism. It was one of the few books spared when Emperor Qin Shi Huang (259-210 B.C.) ordered the burning of previous dynasties' works. The Illustrated Book of Changes is a venerable classic made available to readers of modern Chinese and English. The 64 hexagrams and their traditional commentaries are explained with illustrations, and the Chinese text has been written by leading calligraphers.

These five classic texts have spawned not only Feng Shui, but Tai Chi, Chi-Gong, Acupuncture, and other philosophies and sciences.

The I Ching is one of the primary sources for the calculations of Feng Shui. If you look at a Chinese Luo Pan Compass, the I Ching characters appear to denote the Trigrams. The odd numbers are illustrated by white "sticks" and the even numbers by black "sticks".

For extensive background and detailed description of the I Ching, please see http://en.wikipedia.org/wiki/I_Ching