Overlapping contour lines probably indicate a a. valley b. plain c. cliff d. hill user: the contour interval of a topographic map is 25 feet. how many contour lines will be drawn between sea level and an elevation of 150 feet? a. 3 b. 4 c. 5 d. 6 user: the contour interval of a topographic map is 50 feet, and every fifth line is an index contour. what is the difference in elevation between index contours? a. 50 feet b. 200 feet c. 250 feet d. 350 feet