How to calculate contour interval
![](https://www.thetechedvocate.org/wp-content/uploads/2023/10/what-is-a-contour-interval6-l-660x400.jpg)
When working with topographic maps, one of the most important aspects to understand is the contour interval. The contour interval is the vertical distance between adjacent contour lines on a topographic map. This measurement helps to accurately interpret elevation and overall terrain of the area depicted on the map. In this article, we will discuss how to calculate contour interval in a few simple steps.
Step 1: Identify Contour Lines
The first step in calculating contour interval is to identify all contour lines present on the topographic map. These lines represent areas of equal elevation and are generally represented by different colors or line styles. Pay close attention to distinguish between major and minor contour lines; this information will be crucial in determining the precise contour interval.
Step 2: Locate Index Contours
After identifying all contour lines on the map, locate index contours. These are usually spaced at equal intervals and are often labeled with their corresponding elevation value. Depending on the specific map, index contours could be bold, dashed or have a wider line thickness compared to other contour lines.
Step 3: Count Intervening Contour Lines
Next, choose two consecutive index contours and count the number of intervening contour lines between them. Remember to only count minor or intermediate lines and exclude any others such as major or auxiliary contours.
Step 4: Calculate Vertical Distance Between Index Contours
Now that you have located two consecutive index contours, determine their elevations from labels provided on the map. Subtract the lower elevation from the higher elevation to obtain the vertical distance between these two index contours.
Step 5: Determine Contour Interval
Finally, divide the vertical distance obtained in Step 4 by the number of intervening contour lines counted in Step 3. The resulting value represents your topographic map’s contour interval.
For example:
If the higher elevation index contour is at 1,500 meters and lower elevation index contour is at 1,000 meters, the vertical distance is 500 meters (1500 – 1000 = 500). If there are five intervening contour lines between these two index contours, then:
Contour Interval = Vertical Distance / Intervening Contour Lines
Contour Interval = 500 / 5
Contour Interval = 100 meters
Understanding how to calculate contour interval is an essential skill for any individual working with topographic maps. It allows you to accurately understand and analyze the elevation differences in your area of interest, which in turn, provides valuable information for multiple purposes like hiking, land management or urban planning.