The prime meridian divides the earth into east longitude and west longitude.
Tips
usage
西经 is paired with 东经 dōngjīng (east longitude), and the latitude pair is 北纬 běiwěi / 南纬 nánwěi (north/south latitude). Coordinates read as 西经 + degree + 度: 西经40度 = 40° W. The cutoff is 本初子午线 (the prime meridian, through Greenwich).
memory
经 here is short for 经度 jīngdù (longitude). Visualize the globe as a fabric: 经 (warp threads) run vertically (longitudes), 纬 (weft threads) run horizontally (latitudes) - the metaphor is taken straight from the loom.
