Navigation Term of the Month - Contour lines

Contour lines refer to the thin brown contour lines printed on a topographic map.

The thicker brown lines with numbers are index contour lines and identify the elevation above sea level anywhere along that line.  For example, the index contour labeled 550 is 550 feet above sea level  anywhere along that specific line.  The thinner lines are intermediate contour lines and very by the contour interval published in the map index on the map.  Contour lines close together (bottom right) are steep changes in elevation while lines spaced far apart (top left) represent fairly flat areas.