In Horizon’s Astronomical Charting System, a sector is a cubic cell with each of its edges measuring two 240,000 plethrons (kilometers) in length. Horizon is divided in a total of 125 sectors.
For astronomical and aeronautical convenience, the Horizon has been divided into 5 layers, or planar expanses. Each layer measures 1.200.000 plethrons in length, which is the full length and depth of the Horizon, but only 240.000 in height. When stacked on top one another, they give the full 3d image of the moebius cube that is Horizon.
They are named after the first five letters of the Greek alphabet, from Alpha to Epsilon. Taking after the traditional numbering system of the Mengzi Astronomical Institute, the Alpha Expanse is the expanse in which Mencius is located.
Each expanse in turn, is divided into a horizontal 5×5 grid of cubes, called Sectors. Each Sector has edges of 240.000 plethrons. Sectors are numbered 1-25 for each expanse. Sector 1 of each expanse is always at the perceived center of the expanse, with the rest of the sectors being rated in an outward spiraling clockwise pattern.
Each Sector is divided into an 8x8x8 three-dimensional grid of cubic subdivisions. Each subdivision has edges of 30.000 plethrons. Subdivisions are rated numerically and due to practical navigational reasons, the rating begins from the low left corner of each sector (subdivision 1-1-1) and reaches up to the upper right corner (subdivision 8-8-8).
Navigation - High and Low, Left and Right
Due to the Moebius structure of the Horizon, orientation is mostly a matter of practical agreements rather than a matter of physical parameters. In general, the Alpha expanse is considered to be the lowest expanse, and the Epsilon, the highest. Astronomical left and right, on the other hand, are a matter of etiquette, and the Orientation of the throne of the Mengzi Emperor is used as a point of reference.