Chart

Chart, a sea-map upon which are indicated not only the configuration of rocks and coasts, the nature and characteristics of marks, buoys, and lights, and the set of currents and tides, but the depth of water and the nature of the sea-bottom, with any other particulars that may be of use to navigators. In British charts depths are marked in fathoms of six feet; distances are calculated in cables of one-tenth of a sea-mile. The meridian used is that of Greenwich. Russia, Germany, Sweden, Denmark, Norway, Holland, Austria, and the United States, also use the Greenwich meridian, but France uses that of Paris (which is long. 2° 20' 9.4" E. of Greenwich), and Spain, that of San Fernando, Cadiz (which is long. 6° 12' 16" W. of Greenwich). In foreign charts the depths, or low water soundings, are generally thus expressed: -

The quality of the bottom is usually expressed by some conventional contraction, e.g. r., rock; y., yellow; crl., coral. The invention of charts has been ascribed to John, King of Portugal. Very good English charts were prepared before 1580. The best of them are now constructed under the direction of the Hydrographic Department of the Admiralty, from actual surveys by naval officers and others. They are published by the Admiralty for the information of all who have occasion for them.