Available with 3D Analyst license.
Contours are lines that connect points of equal value (such as elevation, temperature, precipitation, pollution, or atmospheric pressure). The distribution of the lines shows how values change across a surface. Where there is little change in values, the lines are spaced farther apart. Where the values rise or fall rapidly, the lines are closer together.
By following the line of a particular contour, you can identify which locations have the same value. By looking at the spacing of adjacent contours, you can gain a general impression of the gradation of values.
The example below shows an input elevation grid and the output contour map. The areas where the contours are closer together indicate the steeper locations. They correspond with the areas of higher elevation (in white on the input elevation grid).
The attribute table of the contour features contains an elevation attribute for each contour line.