Guidelines for using contour lines effectively on a map?

Understanding Contour Line Spacing

Contour line spacing is critical to interpreting map data. A standard contour interval of 20 feet or 10 meters is common in many maps, but this can vary depending on the map scale and intended use. Identify the contour interval on your map, usually denoted by a key or legend, and use this information to estimate terrain elevation and features. For example, if the contour interval is 20 feet and you see a line every 20 feet, the terrain elevation increases by 20 feet between each line.

Recognizing Terrain Features

Familiarize yourself with common terrain features represented by contour lines, such as ridges, valleys, and peaks. A ridge appears as a series of peaks and troughs, while a valley is marked by a series of saddles (low points) and peaks. Peaks and ridges are usually represented by close contour lines, indicating steep terrain, while valleys and saddles have more space between lines, indicating gentler slopes. Understanding these features will help you anticipate potential route challenges and choose the safest path.

Navigation and Altimeter Use

When using a map and altimeter together, the contour line spacing and altimeter readings will help you navigate and estimate your location. Match your altimeter reading to the contour lines on the map to ensure you’re on the correct terrain elevation. If your altimeter reading is higher than the surrounding contour lines, you may be on a ridge or peak. Conversely, if your reading is lower, you may be in a valley or saddle. This combination of map reading and altimeter data will help you stay oriented and avoid hazards in the terrain.