* Contour Interval: The contour interval is the difference in elevation between adjacent contour lines. In this case, it's 20 feet.
* Spot Elevation: The spot elevation is the exact elevation of a specific point on the map, which is 1237 feet.
To find the first contour line below 1237 feet, subtract the contour interval:
1237 feet - 20 feet = 1217 feet
Therefore, the first contour line below the 1237-foot elevation would be the 1217-foot contour line.
