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Historical C&GS | Nautical Charting

navigation - positioning the survey vessel at sea

There are two major considerations in determining the accuracy and value of the depths printed on a nautical chart.  These are the accuracy of depth measurement and the accuracy with which latitude/longitude values of each respective depth are known.  This second element is constrained by the accuracy with which the surveying vessel has been navigated.

The Coast and Geodetic Survey has always been concerned with assuring that its surveying vessels have been navigated to the highest standards of accuracy.  For most of the first one hundred years of its existence, all determinations of ship position were made by visual means.  Deep ocean surveys and oceanographic studies required using classical astronomic means to position the vessel.  However, for the inshore hydrographic surveys that were the basis of coastal and harbor charts, the primary means of navigation were by the use of the three-point sextant fix or by means of shore observers simultaneously obtaining azimuths with theodolites to the survey vessel. 

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Historical C&GS ~ Nautical Charting Albums
Navigation - Positioning the Survey Vessel At Sea

Visual Navigation

man using sextant

men on signal tower

floating signal
Hydrographic Signals
& Tautwire

signal sign

men using sextants
Sextant Fix
Electronic Navigation

man lowering radio acoustic instrument


navigation instruments
High & Medium

navigation system on lighthouse
Super High

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Last Updated:
October 1, 2009