To find the contour interval of a model that displays topographic contours, you typically examine the labeled contour lines on the model itself or consult any accompanying documentation. If the model has labeled index contour lines, you can calculate the interval using a method similar to finding it on a map.
Understanding Contour Intervals
A contour interval is the vertical distance or difference in elevation between successive contour lines on a map or model. It helps visualize the steepness and shape of the terrain represented. A smaller interval indicates flatter terrain or a more detailed representation, while a larger interval suggests steeper slopes or a less detailed view.
Methods for Finding the Contour Interval on a Model
Often, the contour interval is explicitly stated on the model or in its description. However, if it is not readily available, you can determine it by observing the contour lines.
1. Look for Labeled Index Contour Lines
Similar to topographic maps, models often have index contour lines that are thicker and labeled with their specific elevation values. These are the key to calculating the contour interval if it's not directly stated.
2. Calculate Using Index Contour Lines
This is the most reliable method if labeled index contours are present. It involves finding the elevation difference between two adjacent or non-adjacent index lines and dividing by the number of intervals between them. The reference provided outlines a method for this calculation:
Steps to Calculate the Contour Interval:
- Identify two index contour lines on the model that are labeled with specific elevations. Choose lines that are easy to read.
- Find the difference between the elevations of the two selected index contour lines. Subtract the elevation of the lower index line from the elevation of the higher index line.
- Count the number of intervals (spaces) between the two index contour lines you selected. This includes the regular contour lines between the index lines and the interval before the higher index line.
- Divide the elevation difference (from step 2) by the number of intervals (from step 3). The result is the contour interval.
Here’s a simple way to visualize the calculation:
| Step | Action |
|---|---|
| 1. Select Index Lines | Choose two labeled contour lines (e.g., 500 ft and 600 ft). |
| 2. Calculate Elevation Difference | Higher Elevation - Lower Elevation (e.g., 600 ft - 500 ft = 100 ft). |
| 3. Count Intervals | Count the spaces between the selected index lines. Ensure you count all regular contour lines and the interval leading up to the higher index line. If 5 regular lines are between 500 and 600, there are 5 intervals of the contour interval. |
| 4. Divide | Elevation Difference / Number of Intervals (e.g., 100 ft / 5 intervals = 20 ft). |
In this example, the contour interval of the model would be 20 feet.
3. Examine Regular Contour Lines
If no index contours are labeled, you might sometimes infer the interval by finding any two adjacent labeled contour lines (if any are labeled) or by looking for a pattern in the elevations if multiple lines have labels. This is less common on models than on maps.
Practical Insights
- Consistency: The contour interval is constant across a single model or map.
- Documentation: Always check if the model came with documentation or a legend that specifies the contour interval.
- Visual Estimation: While not a precise method, you can sometimes get a rough idea by visually inspecting the density of lines and any labeled points on the model. Closely spaced lines indicate steepness; widely spaced lines indicate gentle slopes.
By using the calculation method with labeled index contours, you can accurately determine the contour interval used to create the model.
