What do blue lines on a map usually mean?
Blue on a map usually denotes water. Blue lines could be streams and rivers.
It shows whatever is on a map. For example if you have two lines on a map, you wouldn't know what each of the lines mean unless there is a distinction between them. If one was a regular line with no other markings and the other was a line with slashes between them, the key would say what each of the lines stand for. Oh and the key is usually a box.
These lines represent elivation change on the map. The close the lines are together the steeper that area is. In order to know which direction the change is in you have to look at numbers that should be on the lines. if you find two numbers that are on the same slope and compare them you can tell if it is a hill or a valley that is represented on the map.