Which of the following is NOT one of the three types of contour lines?

The correct answer is that "Additional" is not one of the three types of contour lines used in topographic maps. Contour lines are essential for representing elevations and landforms, and they are categorized into three specific types:

Primary contour lines are the main lines that represent changes in elevation and are usually marked with a specific interval, such as every 10 meters. They provide the fundamental structure of the terrain.

Index contour lines are a special type of primary line that is usually thicker and darker, often labeled with their elevation, to make it easier for users to read and understand the elevation changes on the map.

Supplementary contour lines, on the other hand, are used to show additional detail between primary contour lines and are drawn closer together to indicate a steep slope.

The option "Additional" does not correspond to any recognized type of contour line, making it the answer that does not fit within this framework.