Abstract:

The latitude/longitude coordinates of eleven dotted-line segments in The Location Map of the South China Sea Islands (Nanhai zhudao weizhi tu, in Chinese) of the scale 1:4,000,000, produced by the then-Chinese government in 1947, were determined by affine transformation in the geographic information system. Based on this map, a three-dimensional terrain model of the South China Sea was built and then the seafloor topographic characteristics were analyzed with the spatial overlay algorithm. Results show that the lengths and intervals of the dotted-line segments vary with their geographic locations, with larger lengths in the east and smaller lengths in the west. The range and shape of the dotted-line segments, mostly located on the continental slope and shelf, are parallel to the underlying topography. Three principles for demarcation of the dotted line are further summarized: (1) the principle of "equidistance midline" is adopted for the shallow sea basins and canyons; (2) in areas with dramatic reliefs, it follows the axis of troughs; (3) on the southwestern continental slope and shelf of the South China Sea, the shoreline and underlying topography control its distribution. These results could provide the Chinese government a scientific basis for the solution of disputes in the South China Sea.

Key words: the Dotted Line, demarcation, overlapping analysis, submarine topography, affine transformation, South China Sea, China