If the low water line differs considerably from the high water line, then a dotted line represents the low water line. If the bottom in this area is composed of mud, sand, gravel or stones, the type of material will be indicated. If the bottom is composed of coral or rock, then the appropriate symbol will be used. The area alternately covered and uncovered may be shown by a tint which is usually a combination of the land and water tint.
The apparent shoreline shows the outer edge of marine vegetation where that limit would appear as shoreline to the mariner. It is also used to indicate where marine vegetation prevents the mariner from defining the shoreline. A light line symbolizes this shoreline. A broken line marks the inner edge when no other symbol (such as a cliff or levee) furnishes such a limit. The combined land-water tint or the land tint marks the area between inner and outer limits.
NOAA’s National Geodetic Survey (NGS) conducts high accuracy photogrammetric surveys that are used as a basis to update NOAA charts. NGS may also identify shoreline changes from satellite imagery. Some shoreline updates are received through the U.S. Army Corps of Engineers when construction permits have been issued. The shoreline on any particular NOAA nautical may be based on a patchwork of surveys that have been conducted over many years.