**What is the contour interval equal to? Divide the difference in elevation between the index lines by the number of contour lines from one index line to the next. In the example above, the distance 200 is divided by the number of lines, 5. The contour interval is equal to 200 / 5 = 40, or 40-unit contour intervals.**

## How to Determine Contour Interval?

A contour interval is the difference in elevation between contour lines on a map. The larger the contour interval, the further apart the contour lines will be.

The smaller the contour interval, the closer together the contour lines will be. To determine the contour interval of a map, first find two points of known elevation.

Then, using a ruler or other straight edge, draw a line connecting those two points. The difference in elevation between those two points is the contour interval.

For example, if Point A has an elevation of 100 feet and Point B has an elevation of 105 feet, the contour interval would be 5 feet. Keep in mind that the contour interval will be different for different maps, even if they cover the same area.

That‘s because the scale of the map can affect the contour interval. For example, a large–scale map (one that covers a small area in great detail) will have a smaller contour interval than a small–scale map (one that covers a large area in less detail).

To make things even more confusing, some maps use a fractional scale, like 1:24,000, while others use a verbal scale, like “

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