Quick Answer
Index contours signify the frequency of contour lines on a topographic map, typically used to indicate the steepness of terrain. They help map readers quickly identify areas with dense or sparse contour lines, providing a general idea of the land's elevation changes. Index contours are usually denoted by a number, such as "5" or "10", indicating one contour line out of five or ten.
Understanding Index Contours
When analyzing a topographic map, it’s essential to understand index contours. These contours are often represented by a number in the margin of the map, such as “5” or “10”. For example, if a map has an index contour of “5”, it means that every fifth contour line is marked. This can be useful for quickly identifying areas with dense or sparse contour lines.
Interpreting Index Contours in the Field
In the field, index contours can be used to quickly gauge the steepness of terrain. If you’re navigating through a dense forest, for instance, an index contour of “5” may indicate that the terrain is relatively flat, whereas an index contour of “2” may suggest a steeper slope. To accurately interpret index contours, map readers should also consider the contour interval, which is the distance between each contour line. A contour interval of 20 feet, for example, will reveal more detail than a contour interval of 100 feet.
Practical Applications of Index Contours
Index contours are particularly useful for backcountry navigation, where map readers may be relying on their map and compass to navigate. By quickly identifying areas with dense or sparse contour lines, map readers can anticipate potential hazards such as steep slopes or ridges. In addition, index contours can be used to identify potential camp sites, which are often located in areas with relatively flat terrain.
Find more answers
Browse the full Q&A library by topic, or jump back to the topic this question belongs to.