Systematic surveying and chart making date back little more than a century, and most of the information shown on modern charts has been gathered in that time. At present all the principal maritime nations of the world have made, or are extending, careful surveys of their own coasts.
Several of the countries have added valuable contributions in the examination of other regions and oceanic areas beyond their borders. The maritime and colonial interests of Great Britain impelled that nation to carry on extensive surveys along coasts whose inhabitants were not prepared to do this work in the earlier days; the British have made surveys along the coasts of Asia and Africa and a part of South America, and the resulting charts have been a very important and not sufficiently known contribution to commercial intercourse among the nations, as well as to geography.
The Dutch, French, Spanish, and other European governments have made nautical surveys in various parts of the world, largely in connection with their own colonies, and in recent years much useful work has been done by vessels of the German government. The United States has also beyond its own territory made valuable additions to hydrographic knowledge in the work of officers of the Navy in a number of oceanic exploring expeditions, and surveys on the coasts of Mexico and in the West Indies, and in the explorations of Fish Commission vessels.
FIG. 4. EARLY CHART OF NEW YORK HARBOR, 1737.
Extension of maritime surveys. Of the total area of the earth's surface, 51,886,000 square miles is land and 145,054,000 square miles is sea. The oceans thus occupy nearly three-fourths of the whole surface, affording highways open to the nations. To conduct international commerce by water the ships of one country must enter the ports of another. Thus both on the open sea and in the harbors there is an interest, common to seamen of all nationalities, in the advance of marine surveys and in the publication of charts.
To keep the coasts properly charted, as well as lighted and buoyed, is an obligation devolving on modern nations, not only for the benefit of their own commerce but for that of other countries.
As shown below, only a small part of the coast line of the world is thoroughly surveyed. In the extensive ocean areas which are dotted with islands or reefs, a large amount of work is required for their sufficient charting, although many doubtful areas have been cleared up in recent years. Even the parts that are known to be of depths so great as to be free from navigational dangers should be sounded over sufficiently to develop the general configuration of the ocean bottom.