There are several rules that must be followed when determining the elevation of a point that does not fall exactly on a contour line. These rules must be applied correctly when estimating elevation on a military map.

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Rule 6
Benchmarks and spot elevations indicate points of known elevation.

Rule 5
On maps that do not show elevation and relief in as much detail as needed, supplementary contour lines may be used. Marginal information will indicate the interval and type of line.

Rule 4
To determine the elevation of the bottom of a depression, subtract half of the contour interval from the elevation of the lowest contour line around the depression.

Rule 3
To determine the elevation of the top of an unmarked hill, add half the contour interval to the elevation of the highest contour line around the hill.

Rule 2
Point one-fourth to three-fourths the distance from the lower line are considered to be at an elevation half the contour interval above the lower contour line.

Rule 1
Points less than one-fourth the distance between lines are considered to be the same as the elevation of the nearest line.