Part IV.—Marine Surveying and Submarine Contouring
In the days when ocean commerce was borne in relatively small, shallow draft, slow moving sailing vessels, the chart needs of the mariner were limited to a narrow belt along the coast. In fact, the charts extended farther inland during this period than they did seaward. To the seaward the mariner was primarily interested in knowing the correct positions and extent of shoals and reefs that were covered at low tide by less water than the draft of his vessel. Landward he needed complete charts of harbors, bays, and estuaries, however deeply they might indent the coast, and of prominent features along and inland from the shore which were visible from his vessel, and which therefore were of use in fixing the vessel’s position by bearings or angles. Accuracy in position both of landmarks and soundings and depth of water with reference to some datum plane was of first importance. Accuracy in position required triangulation of the highest quality, and accuracy in depth referred to some datum plane necessitated lines of levels connecting permanent tide guage stations. From the needs of control for coastal charts, and with the gradual development of the country, there grew the need for a foundation for surveys of the entire country, and gradually the Coast and Geodetic Survey first order triangulation and precise level nets have been extended to provide the fundamental horizontal and vertical control of the land maps as well as the nautical and aeronautical charts of this country.
With . . .