Directions and positions of systems and nations in the Inner Sphere and Periphery are described relative to their orientation within the galaxy. The derived four main directions are coreward, spinward, rimward and anti-spinward. Though theoretically polar directions, because of the small scale necessary for the Inner Sphere and surroundings, they can be assumed to be linear.
The direction to the galaxy's core is called coreward. It's the Inner Sphere's "north" direction and usually on the top of maps.
Example: The Clan Homeworlds are coreward of the Inner Sphere.
Spinward is the direction of the galaxy's rotation. It represents the "east" direction.
The "south" direction of the known universe is called rimward. It's the direction that points away from the galaxy's center.
Example: The Capellan Confederation occupies the space rimward of Terra.
According to name anti-spinward is the opposite direction of the Milky Way's rotation, representing the Inner Sphere's "west".
- BattleTech Primer, pp. 4-5, Map Legend