What is a contour interval?

• A. The vertical distance between adjacent contour lines on a map
• B. The horizontal distance between two grid lines
• C. The angle between true north and magnetic north
• D. The distance between grid lines on a combat map

Answer: (A)

Contour interval is the vertical difference in elevation between adjacent contour lines on a map. Each contour line represents points at the same elevation, and the interval between those lines is fixed and usually shown in the map legend. This value lets you read elevation changes and assess terrain slope: closely spaced lines indicate a steep slope, while lines spaced far apart indicate a gentler slope. You can use the interval to estimate the height of terrain along a route by counting lines and multiplying by the interval. The other descriptions refer to horizontal spacing of grid lines, magnetic declination (the angle between true north and magnetic north), or grid line spacing—none of which describe elevation changes between contour lines.