A map of a relatively flat area may have a contour interval of 10 feet or less. Maps in mountainous areas may have contour intervals of 100 feet or more. Bathymetric contours are shown in blue or black depending on their location. They show the shape and slope of the ocean bottom surface. The bathymetric contour interval may vary on each map and is explained in the map margin.
Elevations are in feet, based on mean sea level.
Contours are at a basic interval of 1,000 feet. Intermediate contour shown only at 500 feet and 1,500 feet. Dashed contours indicate approximate relief. Elevations are tinted light green, light yellow and yellow, but green color indicates flat or relatively flat terrain regardless of altitude. Areas of unreliable relief are devoid of tint.