To find the highest elevation on a contour map, you need to locate the innermost closed contour line or a marked spot elevation and use the map's contour interval to determine the elevation range or a specific highest possible value.
The highest point on a contour map, typically a hill or mountain peak, is visually represented by:
- Concentric Closed Contour Lines: Look for a series of contour lines that form closed loops, nested one inside the other. The highest point is located within the innermost of these closed loops.
- Spot Elevations: Sometimes, the exact elevation of a peak or specific point is marked directly on the map with a number, often accompanied by a symbol like a triangle (△) or 'X'. This spot elevation is usually the highest point in that immediate area.
Determining the Highest Elevation Value
Once you've located the highest point, you need to understand the contour lines and the contour interval to determine its elevation.
Understanding the Contour Interval
The contour interval is a critical piece of information found on the map legend. As noted in the reference, it tells you the vertical difference in elevation between adjacent contour lines. For example, a map might state the contour interval is 10 meters (as shown in the reference at 1:34). Knowing this interval is essential for calculating elevations.
Reading Contour Line Values
Contour lines are typically labeled with their elevation value. Follow contour lines from known labeled lines to the innermost closed loop to determine its elevation.
Elevation Range
The actual highest elevation of the peak is:
- Higher than the elevation value of the innermost closed contour line.
- Lower than the value of what the next contour line would be if it existed (which is the innermost contour value plus the contour interval).
Calculating the Highest Possible Elevation
To determine the highest possible elevation within the area enclosed by the innermost contour line, especially for a specific point within it (like "Point f" mentioned in the reference around 4:06), a common method is used:
- Highest Possible Elevation = (Elevation of the Innermost Contour Line) + (Contour Interval) - 1 Unit
This calculation gives you the maximum reasonable elevation, assuming the peak doesn't quite reach the elevation of the next potential contour line. The unit subtracted depends on the map's units (e.g., 1 meter if the interval is in meters, 1 foot if in feet).
Practical Example
Let's say the innermost closed contour line on your map is labeled 500 meters, and the map's contour interval is 10 meters (matching the example interval from the reference).
- Highest Contour Value: The innermost contour is 500m.
- Contour Interval: 10m.
- Elevation Range: The highest point is above 500m but below 500m + 10m = 510m. The actual peak elevation is between 500m and 510m.
- Highest Possible Elevation (within the contour): Using the calculation from the reference: 500m + 10m - 1m = 509 meters. This is considered the highest possible elevation for a point or peak located within that 500m contour line.
By identifying the highest closed contour and using the contour interval, you can accurately determine the elevation range of the highest point on a contour map and calculate its highest possible value.
