why alternative shades are done in graphical scale in cartography
Hello,
Cartography is mainly art and science which is represented graphically geographical area.
So choosing colour is very carefully ensures that the map is intuitive and easy to read. This process is referred to as feature association. Also, the cartographer must take into account that many people have impaired colour vision, and colours must be used that are easily distinguishable by such readers. So that's why use the alternative shades.
All the best.