On the four-dimensional map, purple is used to represent saline-alkali land. According to relevant data, the general color sequence of layered color setting is that the ocean is blue, the plain is green, the low hills are yellow, the mountains and plateaus are brown, and the snow, salt and alkali and glaciers are light purple. Different shades of blue are painted between different isobaths, which can be used to indicate the depth of the seabed. Between different contour lines, the thicker the green, the lower the terrain and the deeper the brown, indicating the higher the terrain, and the area above the snow line is usually represented by white.