What does the red sailboat mean on the map?

Represents the navigable waters and their vicinity. According to relevant public information, red sailboats are placed in the navigable waters and their vicinity on the map, which are used to represent navigation channels, anchorages, obstacles, shoals, etc. , or as a sign of positioning and steering, etc. A map is a graph or image that selectively shows some phenomena of the earth on a plane or a sphere in two-dimensional or multi-dimensional forms and means according to certain laws. It has strict mathematical foundation, symbol system and text annotation.