|Maps for Mariners
Charts for Marylanders
The Language of Charts
The Language of Charts
A chart must display a wide variety of information about
the body of water it describes. In order to efficiently indicate
all relevant facts in one diagram, the chartmaker must use symbols as a
form of shorthand. To read a chart, one must understand what all
these symbols mean.
Before symbols were standardized by the U.S. Coast Survey
and subsequent government agencies, chartmakers freely invented their own.
Here are some examples.
|Rose of the Winds
The compass rose is perhaps the most important symbol
on any chart. It provides the mariner a reference for determinng his position
by indicating the thirty-two points of the compass.
The compass rose symbol reflects the directions of the
wind. Early chartmakers devised the basic rose by indicating the direction
of the four known winds -- north, south, east, and west.
The four winds became twelve as mariners recognized the
variety of directions from which the wind actually blew. By the sixteenth
century the rose indicated thirty-two winds, with eight primary winds subdivided
into half-winds and again into quarter-winds.
The modern compass rose is a combination of the ancient
rose of the winds and a reference indicating magnetic variation, or the
angle between magnetic and true north.
Note the compass rose symbols on each chart in this exhibition.Compare
the artistry of the early roses with the technical roses of modern charts.
||Pas Caerte Van Nieu Nederlandt en de Engelsche
Virginies Van Cabo Cod tot Cabo Canrick
Huntingfield Corporation Collection, MSA SC 1399-1-474
Dutch sea charts were about the only published charts
available in the late seventeenth century. This one, like most others,
has no soundings; it shows only sketchy shoals and is not based on original
surveying. Its elaborate system of rhumb lines could give a navigator some
idea of where he would strike land if a given course were taken. The only
other symbol to assist the mariner is the compass rose, shown at that time
without magnetic variation or change. A ship relying on this chart for
transoceanic passage would have been lucky to survive.
||A Survey of the Chesapeake
Anthony De Mayne
Reproduction from the Library of Congress
Huntingfield Corporation Map Collection, MSA SC1399-1-184
This 1820 British Admiralty chart was based on surveys
made in 1814. It contains a great deal of coded information for the navigator.
Arrows indicate the direction of current flow; anchors indicate anchorages;
and shoreline profiles assist with coast piloting. This chart also gave
the most complete navigational light data of that time and indicated bottom
conditions and prominent landmarks.
||The Harbor of Annapolis
U.S. Coast Survey
Washington, DC, 1846
Huntingfield Corporation Map Collection, MSA SC 1399-618
This was the first U.S. Coast Survey chart of any part
of the Chesapeake Bay. It features a number of symbols which were incorporated
into later charts. Stippling indicates depth changes and single lines mark
channels. Arrows indicate the direction and strength of ebb and flow tides.
The chart also includes detailed topography, shoreline profiles, tidal
notes, magnetic variation, and sailing directions.
© Copyright May 23, 2017Maryland State Archives