As feng shui was refined over long ages, it divided broadly into two ways of seeing. One is the form school and the other is the compass school. Even when gazing at the same land, the grain of the reading differed according to what was examined first and where weight was placed; rather than rival answers, the two are better understood as two perspectives for reading feng shui.
The form school is the current that finds auspicious ground by observing with the eye the outward shapes formed by mountains and water. It examines how a ridge runs down and gathers energy, how a watercourse winds and embraces a site, and whether the surrounding peaks cradle the place or scatter it. In likening the lay of the mountains to a dragon and reading its flow, in gauging the spot where energy settles, and in seeing whether the hills around the left, right, and front enclose the site well, the form school prizes above all the shape and structure of the land. In a word, it is a feng shui confirmed by walking and seeing with the eye.
The compass school, by contrast, puts forward principle and calculation such as yin and yang, the five phases, direction, and the cyclical signs. For the same spot it weighs which way one sets the back and which way one faces, and how that direction accords with the resident or the time, in order to reckon fortune. For this it used a feng shui compass to divide and read directions finely, placing weight on discerning the principle and order dwelling within the land rather than on outward form. If the form school is a feng shui seen with the eye, the compass school may be likened to a feng shui reckoned by principle.
Historically the center of gravity between the two currents is said to have shifted with the times. From Goryeo to early Joseon, an eye centered on directly examining the forms of mountains and rivers stood out, while from the middle of Joseon onward compass-school methods that reckoned with direction and principle spread widely and came to be used alongside it. Yet it is natural to understand this change not as one side pushing out the other, but as a broadening of the interests and tools of those who practiced feng shui.
In actual practice the two branches were more often used together, complementing each other, than apart. One would first examine the forms of mountains and water by the form school to choose the spot where energy settles, and then at that chosen spot gauge a fitting direction by the compass school. This arrangement, finding the site by form and setting the direction by principle, shows well that the two perspectives originally branched from a single root.
Therefore, rather than declaring outright which of the form and compass schools is correct, it is a way to a broad understanding of feng shui to receive them as two gazes that read the same land along different grains. Only when an eye that prizes the appearance of nature and a mind that discerns the order within it come together was feng shui held to be a balanced insight, leaning to neither side.
Looking a little more closely at what grain each branch actually reckoned with makes the difference clearer still. The form school commonly examines four things in turn: the dragon, the node, the surrounding hills, and the water. It sees how the dragon, the ridge that carries energy as it flows down, winds and stretches; it gauges the node, the single point where that energy at last settles; it weighs whether the surrounding hills, the nearby mountain forms that enclose and protect the node, wrap the site well; and it reckons step by step how the water, the watercourse that halts the energy, curves and flows away from the site. All of this leans on an eye that looks at and reads directly the shapes of mountains and water. The compass school, by comparison, reckons direction with a feng shui compass held in the hand. Around the rim of the compass are inscribed twenty-four directions that divide the cardinal points more finely, so that it reads in detail which way the site sets its back and which way it faces, and from which direction the water comes and goes, matching this against the principle of yin-yang and the five phases to weigh fortune. For the same land, then, one side approached with foot and eye, the other with compass and calculation.