How many types of contour lines are there on a map?

Contour lines on a map are used to represent the elevation and shape of the terrain. There are three distinct types of contour lines:

1. Index Contour Lines: These are usually thicker and darker lines that are labeled with their elevation, making it easy for users to quickly interpret the height of the land. They typically appear at regular intervals, such as every fifth contour line.

2. Intermediate Contour Lines: These lines fall between the index contours and are thinner. They help provide additional detail about the terrain's elevation changes but are not labeled with their specific elevation.

3. Supplementary Contour Lines: These lines are dashed or dotted and indicate a lower elevation than the adjacent intermediate contours. They are used in areas where the terrain is relatively flat or where closely spaced elevation changes occur.

Understanding these types of contour lines is crucial for interpreting a topographic map, allowing for an accurate visual representation of the landscape's features and helping in planning navigation or land use effectively.