In the old day, there were only two Feng Shui schools, namely, Feng Shui Forms School and Feng Shui Compass School. The Compass Schools also known as Liqi. 理氣 school or Formula school. These two Feng Shui schools work together as Liqi need forms and forms need Liqi.
In term of Feng Shui Forms School, it is the way of looking at the surrounding forms, such as hills, mountains, buildings, towers, rivers, bridges, roads, streets and so on. Feng Shui Forms school is very consistency among different Feng Shui Masters. A mountain at the left is a mountain at the left. A river flows to the west is a river flows to the west. There are no discrepancies about Feng Shui forms.
However, when come to talking about Liqi, there are so many different styles or formulas schools. To name a few, they are:
Flying Stars 3 Yuen 9 Periods Feng Shui Liqi
Triple Harmony (San He) Feng Shui Liqi
San Yeun Feng Shui Liqi
8 Eight House Feng Shui Liqi
Four Pillars Personal Feng Shui Liqi
Da Gwa Feng Shui Liqi
And many more. You can read more here
Strictly speaking, Feng Shui forms and feng shui formula cannot be applied separately. Just like Yin and Yang, they mutually coexist. No matter which Feng Shui Liqi / formula you are using, the Feng Shui Forms and Compass school relies on each other.
Here is my experience.
The relationship of Feng Shui forms and Liqi
Good Feng Shui forms need good Liqi to produce good Feng Shui result.
Bad Feng Shui forms with good Liqi never produces positive results.
Good Feng Shui forms can reduce the effect of bad Liqi.
Bad form with bad Liqi brings disaster feng shui results.
From the above, good forms or good surroundings is ultra important in Feng Shui.
In short, Good forms are always the priority to select a good Feng Shui site or Feng Shui house.