A grading plan shows contour lines at 2-foot intervals. If you count 5 contour lines between two points, what is the elevation difference?
Correct Answer
D) 10 feet
With contour lines at 2-foot intervals, each line represents a 2-foot elevation change. Five contour lines represent 5 × 2 = 10 feet of elevation difference between the two points.
Why This Is the Correct Answer
Contour lines represent lines of equal elevation, and the interval between adjacent contour lines indicates the vertical distance between them. When a grading plan specifies 2-foot intervals, each contour line represents a 2-foot change in elevation from the next line. To find the total elevation difference between two points, you multiply the number of contour lines crossed by the contour interval. With 5 contour lines at 2-foot intervals, the calculation is 5 × 2 = 10 feet.
Why the Other Options Are Wrong
Option A: 12 feet
This answer appears to be a miscalculation, possibly confusing the number of spaces between lines (4) with the total elevation change calculation.
Option B: 8 feet
This answer incorrectly calculates the elevation difference, possibly by adding extra intervals or misunderstanding the relationship between contour lines and elevation change.
Option C: 5 feet
This answer incorrectly assumes each contour line represents 1 foot of elevation change, ignoring the specified 2-foot interval.
Memory Technique
Remember 'Lines × Interval = Total' - always multiply the number of contour lines by the stated interval to get the elevation difference.
Reference Hint
Look up site work and grading sections in construction reference materials, typically found in surveying or site preparation chapters.
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