Meridian Coordinates [ SAFE - 2026 ]

To a layperson, "ST-44" is a code. To an acupuncturist, it is a specific location: On the foot, in the web between the 2nd and 3rd toes, proximal to the margin of the web. But coordinates do more than locate—they predict function.

Unlike metric inches or centimeters, a Cun changes size based on the individual’s body.

Therefore, the meridian coordinate PC-6 (Pericardium 6) is universally described as "2 Cun proximal to the transverse crease of the wrist." This means you measure the patient’s thumb width, double it, and move toward the elbow.

Why not just say "press the middle of the forearm"? Because anatomy varies. A person with a 12-inch forearm has different "2 Cun" than a person with an 8-inch forearm. The coordinate system ensures proportional accuracy. meridian coordinates

In map projections (like UTM), a central meridian defines the origin for eastings.
Coordinates are given in meters relative to that meridian.

If you meant something else — like meridian coordinate system for acupuncture/energy meridians, or a specific data format — could you clarify? I’d be happy to give a more precise answer.

For centuries, the lack of a standardized "zero meridian" was a logistical nightmare. Sailors and cartographers used various reference points based on their home nations; the French used Paris, the Spanish used Cadiz, and the British used Greenwich. It was not until the International Meridian Conference of 1884 that Greenwich, London, was largely adopted as the Prime Meridian (0° longitude). To a layperson, "ST-44" is a code

This decision did more than just standardize maps; it synchronized the world. Meridian coordinates are intrinsically linked to time. Because the Earth rotates 360 degrees in approximately 24 hours, every 15 degrees of longitude represents a one-hour time difference. The meridian system allowed humanity to move from local solar time—where noon is whenever the sun is directly overhead—to a standardized global time system. Without meridian coordinates, the scheduling of trains, global commerce, and international communication would be impossible.

In astronomy, the meridian is the great circle passing through the celestial poles and an observer's zenith.
When combined with a coordinate system:

Example:
If your local sidereal time = object's RA → object is on the meridian. Therefore, the meridian coordinate PC-6 (Pericardium 6) is

To understand meridian coordinates, one must first understand the geometry of the Earth. A meridian is not a full circle, but a semi-circle—an imaginary arc running from the geographic North Pole to the geographic South Pole. Unlike lines of latitude, which are parallel and never meet, every meridian intersects at the poles. This specific geometry dictates how they function as coordinates.

While latitude is measured in degrees north or south of the Equator (a naturally occurring midpoint between the poles), longitude (the coordinate derived from meridians) has no natural zero point. The Earth spins on an axis, offering a physical reference for north and south, but it does not naturally distinguish east from west. Therefore, the definition of meridian coordinates relies entirely on an arbitrary, political, and historical choice: the Prime Meridian.